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  • Apache and fastcgi - How to secure an Apache server with fastcgi enabled?

    - by skyeagle
    I am running a headless server on Ubuntu 10.x. I am running Apache 2.2. I am writing a fastcgi application for deployment on the server. I remember reading a while back (I could be wrong) that running CGI (and by implication fastcgi) on a server, can provide 'backdoors' for potential attackers - or at the very least, could compromise the server if certain security measurements are not taken. My questions are: what are the security 'gotcha's that I have to be aware of if I am enabling mod_fastcgi on my Apache server? I want to run the fastcgi as a specific user (with restricted access) how do I do this?

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  • Listing the routing table takes long time to complete

    - by Rafal Rawicki
    When I print routes defined on my computer using route, it takes about 5 to 20 seconds to complete. Why does it take so much time? With VPN enabled: $ time sudo route Kernel IP routing table (...) real 0m21.423s user 0m0.000s sys 0m0.012s With no VPN, this is about 5 seconds - still, computer can do a lot in this time. I've repeated my measurements few times, getting very similar results each try. My machine is Ubuntu with 3.0.0 kernel, but as far as I know, route on the other computers works the same way.

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  • Excel - graphing mean and standard deviation

    - by joe_shmoe
    Hi all, I have measurements for multiple devices, and have their mean and sd values. I would like to produce a chart that would show these values, and I think the best would be if I could have something that looks like a bar chart(-ish) - the device names in x axis, values in y axis, and for each device to have a 'floating' bar that would represent values (mean - sd :: mean + sd), and some marker in the middle to show the actual mean value. is it doable? or would you suggest some other chart? Thanks a lot

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  • Signal strength and Speed of wireless network

    - by Tim
    As shown by Lenovo Access Connections on my Windows 7, the wireless network I am using has a speed of 54.0Mbps but a signal strength of 88%. I am using WinSCP with unlimited speed to download files. WinSCP shows that the speed fluctuates between 100 and 120KiB/s. I was wondering what are the difference between the two speeds from Lenovo Access Connections and WinSCP? How can I tell the actual speed performance, for example, from the above measurements: speeds and the signal strength mentioned in the two places. Thanks and regards!

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  • Signal strength and Speed of wireless network

    - by Tim
    As shown by Lenovo Access Connections on my Windows 7, the wireless network I am using has a speed of 54.0Mbps but a signal strength of 88%. I am using WinSCP with unlimited speed to download files. WinSCP shows that the speed fluctuates between 100 and 120KiB/s. I was wondering what are the difference between the two speeds from Lenovo Access Connections and WinSCP? How can I tell the actual speed performance, for example, from the above measurements: speeds and the signal strength mentioned in the two places. Thanks and regards!

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  • Apache and fastcgi - How to secure an Apache server with fastcgi enabled?

    - by skyeagle
    I am running a headless server on Ubuntu 10.x. I am running Apache 2.2. I am writing a fastcgi application for deployment on the server. I remember reading a while back (I could be wrong) that running CGI (and by implication fastcgi) on a server, can provide 'backdoors' for potential attackers - or at the very least, could compromise the server if certain security measurements are not taken. My questions are: what are the security 'gotcha's that I have to be aware of if I am enabling mod_fastcgi on my Apache server? I want to run the fastcgi as a specific user (with restricted access) how do I do this?

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  • How to "paint" the data layer of a CD using a CD drive?

    - by Jens
    I am looking for software to "paint" geometric shapes, dots or lines on the data layer of a writable CD (or DVD) using a standard drive. These do not have to be visible to the naked eye; I'd try to abuse the small dot size on the CD for some scientific measurements. I am aware of the "LightScribe" feature of some drives and that is not what I am looking for. Most of the software available is of course limited to write music or data, on does not offer the low-level "place a dot at this radius, this angle"-functionality. Is there something out there for me?

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  • Any reasonable UPS for a Desktop PC, just to shut it down?

    - by Michael Stum
    While I do have a surge protector to protect against overvoltage (hopefully), I have nothing against undervoltage. When a lightning storm hits, I had the lights flickering at some point. The PC continued to run, but it got me thinking of getting a UPS as a way to a) have a clean 120V/60Hz power source and b) have a way to shut down the PC in case something bad happens. I heard not all UPS' protect against power spikes, so I wonder if someone has a recommendation? It does not need to keep the PC on for a long time if the power goes out, it's good enough if it shuts down the PC after 5 minutes or so. There are 2 PCs connected. One is a Core i7-860 with a Radeon 5870 running Windows 7 Ultimate (so quite power hungry. It uses a 600W PSU but I have no measurements of the actual usage), the other one is a Windoes Home Server, running WHS/Windows Server 2003. Any recommendations in the low-price segment?

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  • Total network data sent/received of a non-daemon Linux process?

    - by leden
    I'm looking for a simple and effective way of measuring total bytes received/sent from a single process upon its termination. Basically, I am looking for a tool which has the interface similar to "time" and "/usr/bin/time", e.g. measure-net-data <prog_to_run> <prog_args> Received (b): XYZ Sent (b): ABC I know that there are many tools for bandwidth/network monitoring, but as far I can tell all of them are performing the measurements it real-time, which is inappropriate not only because of overhead but also because of the inconvenience - I would need to stop the program, capture the output of the tool and then kill it. I have seen that newer versions of Linux 2.6.20+ provide /proc/<pid>/io/ which contain the information I'm looking for; however, everything under /proc/<pid> when the process terminates, so I'm again back to the same problem as with any network monitoring tool.

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  • What's the best license for my website?

    - by John Maxim
    I have developed a unique website but do not have a lot of fund to protect it with trademark or patents. I'm looking for suggestions so that when my supervisor gets my codes, some laws restrict anyone from copying it and claim their work. I'm in the middle of thinking, making the application a commercial one or never allowing it to be copied at all. What kind of steps am I required to take in order to make full measurements so my applications are fully-protected? I've come across a few, one under my consideration is MIT license. Some say we can have a mixture of both commercial and MIT. I would also like to be able to distribute some functions so it can be modified by others but I'd still retain the ownership. Last but not least, it's confusing when I think of protecting the whole website, and protecting codes by codes in division. How should we go about this? Thanks. N.B I have to pass it over to the supervisor as this is a Uni project. I need this to be done within 2 weeks. So time to get my App protected is a factor here.

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  • Wolfram is out, any alternatives? Or how to go custom?

    - by Patrick
    We were originally planning on using wolfram alpha api for a new project but unfortunately the cost was entirely way to high for what we were using it for. Essentially what we were doing is calculating the nutrition facts for food. (http://www.wolframalpha.com/input/?i=chicken+breast+with+broccoli). Before taking the step of trying to build something that may work in its place for this use case is there any open source code anywhere that can do this kind of analysis and compile the data? The hardest part in my opinion is what it has for assumptions and where it gets that data to power the calculations. Or another way to put it is, I cannot seem to wrap my head around building something that computes user input to return facts and knowledge. I know if I can convert the user input into some standardized form I can then compare that to a nutrition fact database to pull in the information I need. Does anyone know of any solutions to re-create this or APIs that can provide this kind of analysis? Thanks for any advice. I am trying to figure out if this project is dead in the water before it even starts. This kind of programming is well beyond me so I can only hope for an API, open source, or some kind of analysis engine to interpret user input when I know what kind of data they are entering (measurements and food).

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  • Complex string matching with fuzzywuzzy

    - by That1Guy
    I'm attempting to write a process that matches obscure strings to a single 'master string' for further processing. I have a lot of data that looks something like this: Basketball Basket Ball Football BasketBallR BBall BBall - r FootB ...and so on. These need to be mapped to a master record like so: Basketball = Basket Ball, BBall Basketball - R = BasketBallR, BBall - r I also have instances of data resembling this format: Football -r FootBall - r-g/H,Q,HH These situations need to be separated into different categories before being mapped. For example FootBall - r-g/H,Q,HH should be: Football - r Football - g Football - H Football - Q Football - HH At this point, it still needs to be mapped to a master record... I've tried several different combinations of fuzzywuzzy matching methods, Levenshtein Distance measurements, regex, etc. and can't seem to find a reliable method to logically associate different naming styles of a single item with a master name. I'm throwing my hands up in desperation. Are there any existing python resources than can help sort out my problem? Are there other options? Can anybody point out an obvious option that I might have overlooked? Basically, any suggestion, solution, resource or alternative method is greatly appreciated.

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  • Algorithms for Data Redundancy and Failover for distributed storage system?

    - by kennetham
    I'm building a distributed storage system that works with different storage sizes. For instance, my storage devices have sizes of 50GB, 70GB, 150GB, 250GB, 1000GB, 5 storage systems in one system. My application will store any files to the storage system. Question: How can I build a distributed storage with the idea of data redundancy and fail-over to store documents, videos, any type of files at the same time ensuring that should one of any storage devices fail, there would be another copy of these files on another storage device. However, the concern is, 50GB of storage can only store this maximum number of files as compared to 70GB, 150GB etc. With one storage in mind, bringing 5 storage systems like a cloud storage, is there any logical way to distribute or store the files through my application? How do I ensure data redundancy through different storage sizes? Is there any algorithm to collate multiple blob files into a single file archive? What is the best solution for one cloud storage with multiple different storage sizes? I open this topic with the objective of discussing the best way to implement this idea, assuming simplicity, what are the issues of this implementation, performance measurements and discussion of the limitations.

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  • Static vs. dynamic memory allocation - lots of constant objects, only small part of them used at runtime

    - by k29
    Here are two options: Option 1: enum QuizCategory { CATEGORY_1(new MyCollection<Question>() .add(Question.QUESTION_A) .add(Question.QUESTION_B) .add...), CATEGORY_2(new MyCollection<Question>() .add(Question.QUESTION_B) .add(Question.QUESTION_C) .add...), ... ; public MyCollection<Question> collection; private QuizCategory(MyCollection<Question> collection) { this.collection = collection; } public Question getRandom() { return collection.getRandomQuestion(); } } Option 2: enum QuizCategory2 { CATEGORY_1 { @Override protected MyCollection<Question> populateWithQuestions() { return new MyCollection<Question>() .add(Question.QUESTION_A) .add(Question.QUESTION_B) .add...; } }, CATEGORY_2 { @Override protected MyCollection<Question> populateWithQuestions() { return new MyCollection<Question>() .add(Question.QUESTION_B) .add(Question.QUESTION_C) .add...; } }; public Question getRandom() { MyCollection<Question> collection = populateWithQuestions(); return collection.getRandomQuestion(); } protected abstract MyCollection<Question> populateWithQuestions(); } There will be around 1000 categories, each containing 10 - 300 questions (100 on average). At runtime typically only 10 categories and 30 questions will be used. Each question is itself an enum constant (with its fields and methods). I'm trying to decide between those two options in the mobile application context. I haven't done any measurements since I have yet to write the questions and would like to gather more information before committing to one or another option. As far as I understand: (a) Option 1 will perform better since there will be no need to populate the collection and then garbage-collect the questions; (b) Option 1 will require extra memory: 1000 categories x 100 questions x 4 bytes for each reference = 400 Kb, which is not significant. So I'm leaning to Option 1, but just wondered if I'm correct in my assumptions and not missing something important? Perhaps someone has faced a similar dilemma? Or perhaps it doesn't actually matter that much?

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  • How can I convince my boss that ANSI C is inadequate for our new project?

    - by justifiably cowardly
    A few months ago, we started developing an app to control an in-house developed test equipment and record a set of measurements. It should have a simple UI, and would likely require threads due to the continuous recording that must take place. This application will be used for a few years, and shall be maintained by a number of computer science students during this period. Our boss graduated some 30 years ago (not to be taken as an offense; I have more than half that time on my back too) and has mandated that we develop this application in ANSI C. The rationale is that he is the only one that will be around the entire time, and therefore he must be able to understand what we are doing. He also ruled that we should use no abstract data types; he even gave us a list with the name of the global variables (sigh) he wants us to use. I actually tried that approach for a while, but it was really slowing me down to make sure that all pointer operations were safe and all strings had the correct size. Additionally, the number of lines of code that actually related to the problem in hand was a only small fraction of our code base. After a few days, I scrapped the entire thing and started anew using C#. Our boss has already seen the program running and he likes the way it works, but he doesn't know that it's written in another language. Next week the two of us will meet to go over the source code, so that he "will know how to maintain it". I am sort of scared, and I would like to hear from you guys what arguments I could use to support my decision. Cowardly yours,

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  • Is Social Media The Vital Skill You Aren’t Tracking?

    - by HCM-Oracle
    By Mark Bennett - Originally featured in Talent Management Excellence The ever-increasing presence of the workforce on social media presents opportunities as well as risks for organizations. While on the one hand, we read about social media embarrassments happening to organizations, on the other we see that social media activities by workers and candidates can enhance a company’s brand and provide insight into what individuals are, or can become, influencers in the social media sphere. HR can play a key role in helping organizations make the most value out of the activities and presence of workers and candidates, while at the same time also helping to manage the risks that come with the permanence and viral nature of social media. What is Missing from Understanding Our Workforce? “If only HP knew what HP knows, we would be three-times more productive.”  Lew Platt, Former Chairman, President, CEO, Hewlett-Packard  What Lew Platt recognized was that organizations only have a partial understanding of what their workforce is capable of. This lack of understanding impacts the company in several negative ways: 1. A particular skill that the company needs to access in one part of the organization might exist somewhere else, but there is no record that the skill exists, so the need is unfulfilled. 2. As market conditions change rapidly, the company needs to know strategic options, but some options are missed entirely because the company doesn’t know that sufficient capability already exists to enable those options. 3. Employees may miss out on opportunities to demonstrate how their hidden skills could create new value to the company. Why don’t companies have that more complete picture of their workforce capabilities – that is, not know what they know? One very good explanation is that companies put most of their efforts into rating their workforce according to the jobs and roles they are filling today. This is the essence of two important talent management processes: recruiting and performance appraisals.  In recruiting, a set of requirements is put together for a job, either explicitly or indirectly through a job description. During the recruiting process, much of the attention is paid towards whether the candidate has the qualifications, the skills, the experience and the cultural fit to be successful in the role. This makes a lot of sense.  In the performance appraisal process, an employee is measured on how well they performed the functions of their role and in an effort to help the employee do even better next time, they are also measured on proficiency in the competencies that are deemed to be key in doing that job. Again, the logic is impeccable.  But in both these cases, two adages come to mind: 1. What gets measured is what gets managed. 2. You only see what you are looking for. In other words, the fact that the current roles the workforce are performing are the basis for measuring which capabilities the workforce has, makes them the only capabilities to be measured. What was initially meant to be a positive, i.e. identify what is needed to perform well and measure it, in order that it can be managed, comes with the unintended negative consequence of overshadowing the other capabilities the workforce has. This also comes with an employee engagement price, for the measurements and management of workforce capabilities is to typically focus on where the workforce comes up short. Again, it makes sense to do this, since improving a capability that appears to result in improved performance benefits, both the individual through improved performance ratings and the company through improved productivity. But this is based on the assumption that the capabilities identified and their required proficiencies are the only attributes of the individual that matter. Anything else the individual brings that results in high performance, while resulting in a desired performance outcome, often goes unrecognized or underappreciated at best. As social media begins to occupy a more important part in current and future roles in organizations, businesses must incorporate social media savvy and innovation into job descriptions and expectations. These new measures could provide insight into how well someone can use social media tools to influence communities and decision makers; keep abreast of trends in fast-moving industries; present a positive brand image for the organization around thought leadership, customer focus, social responsibility; and coordinate and collaborate with partners. These measures should demonstrate the “social capital” the individual has invested in and developed over time. Without this dimension, “short cut” methods may generate a narrow set of positive metrics that do not have real, long-lasting benefits to the organization. How Workforce Reputation Management Helps HR Harness Social Media With hundreds of petabytes of social media data flowing across Facebook, LinkedIn and Twitter, businesses are tapping technology solutions to effectively leverage social for HR. Workforce reputation management technology helps organizations discover, mobilize and retain talent by providing insight into the social reputation and influence of the workforce while also helping organizations monitor employee social media policy compliance and mitigate social media risk.  There are three major ways that workforce reputation management technology can play a strategic role to support HR: 1. Improve Awareness and Decisions on Talent Many organizations measure the skills and competencies that they know they need today, but are unaware of what other skills and competencies their workforce has that could be essential tomorrow. How about whether your workforce has the reputation and influence to make their skills and competencies more effective? Many organizations don’t have insight into the social media “reach” their workforce has, which is becoming more critical to business performance. These features help organizations, managers, and employees improve many talent processes and decision making, including the following: Hiring and Assignments. People and teams with higher reputations are considered more valuable and effective workers. Someone with high reputation who refers a candidate also can have high credibility as a source for hires.   Training and Development. Reputation trend analysis can impact program decisions regarding training offerings by showing how reputation and influence across the workforce changes in concert with training. Worker reputation impacts development plans and goal choices by helping the individual see which development efforts result in improved reputation and influence.   Finding Hidden Talent. Managers can discover hidden talent and skills amongst employees based on a combination of social profile information and social media reputation. Employees can improve their personal brand and accelerate their career development.  2. Talent Search and Discovery The right technology helps organizations find information on people that might otherwise be hidden. By leveraging access to candidate and worker social profiles as well as their social relationships, workforce reputation management provides companies with a more complete picture of what their knowledge, skills, and attributes are and what they can in turn access. This more complete information helps to find the right talent both outside the organization as well as the right, perhaps previously hidden talent, within the organization to fill roles and staff projects, particularly those roles and projects that are required in reaction to fast-changing opportunities and circumstances. 3. Reputation Brings Credibility Workforce reputation management technology provides a clearer picture of how candidates and workers are viewed by their peers and communities across a wide range of social reputation and influence metrics. This information is less subject to individual bias and can impact critical decision-making. Knowing the individual’s reputation and influence enables the organization to predict how well their capabilities and behaviors will have a positive effect on desired business outcomes. Many roles that have the highest impact on overall business performance are dependent on the individual’s influence and reputation. In addition, reputation and influence measures offer a very tangible source of feedback for workers, providing them with insight that helps them develop themselves and their careers and see the effectiveness of those efforts by tracking changes over time in their reputation and influence. The following are some examples of the different reputation and influence measures of the workforce that Workforce Reputation Management could gather and analyze: Generosity – How often the user reposts other’s posts. Influence – How often the user’s material is reposted by others.  Engagement – The ratio of recent posts with references (e.g. links to other posts) to the total number of posts.  Activity – How frequently the user posts. (e.g. number per day)  Impact – The size of the users’ social networks, which indicates their ability to reach unique followers, friends, or users.   Clout – The number of references and citations of the user’s material in others’ posts.  The Vital Ingredient of Workforce Reputation Management: Employee Participation “Nothing about me, without me.” Valerie Billingham, “Through the Patient’s Eyes”, Salzburg Seminar Session 356, 1998 Since data resides primarily in social media, a question arises: what manner is used to collect that data? While much of social media activity is publicly accessible (as many who wished otherwise have learned to their chagrin), the social norms of social media have developed to put some restrictions on what is acceptable behavior and by whom. Disregarding these norms risks a repercussion firestorm. One of the more recognized norms is that while individuals can follow and engage with other individual’s public social activity (e.g. Twitter updates) fairly freely, the more an organization does this unprompted and without getting permission from the individual beforehand, the more likely the organization risks a totally opposite outcome from the one desired. Instead, the organization must look for permission from the individual, which can be met with resistance. That resistance comes from not knowing how the information will be used, how it will be shared with others, and not receiving enough benefit in return for granting permission. As the quote above about patient concerns and rights succinctly states, no one likes not feeling in control of the information about themselves, or the uncertainty about where it will be used. This is well understood in consumer social media (i.e. permission-based marketing) and is applicable to workforce reputation management. However, asking permission leaves open the very real possibility that no one, or so few, will grant permission, resulting in a small set of data with little usefulness for the company. Connecting Individual Motivation to Organization Needs So what is it that makes an individual decide to grant an organization access to the data it wants? It is when the individual’s own motivations are in alignment with the organization’s objectives. In the case of workforce reputation management, when the individual is motivated by a desire for increased visibility and career growth opportunities to advertise their skills and level of influence and reputation, they are aligned with the organizations’ objectives; to fill resource needs or strategically build better awareness of what skills are present in the workforce, as well as levels of influence and reputation. Individuals can see the benefit of granting access permission to the company through multiple means. One is through simple social awareness; they begin to discover that peers who are getting more career opportunities are those who are signed up for workforce reputation management. Another is where companies take the message directly to the individual; we think you would benefit from signing up with our workforce reputation management solution. Another, more strategic approach is to make reputation management part of a larger Career Development effort by the company; providing a wide set of tools to help the workforce find ways to plan and take action to achieve their career aspirations in the organization. An effective mechanism, that facilitates connecting the visibility and career growth motivations of the workforce with the larger context of the organization’s business objectives, is to use game mechanics to help individuals transform their career goals into concrete, actionable steps, such as signing up for reputation management. This works in favor of companies looking to use workforce reputation because the workforce is more apt to see how it fits into achieving their overall career goals, as well as seeing how other participation brings additional benefits.  Once an individual has signed up with reputation management, not only have they made themselves more visible within the organization and increased their career growth opportunities, they have also enabled a tool that they can use to better understand how their actions and behaviors impact their influence and reputation. Since they will be able to see their reputation and influence measurements change over time, they will gain better insight into how reputation and influence impacts their effectiveness in a role, as well as how their behaviors and skill levels in turn affect their influence and reputation. This insight can trigger much more directed, and effective, efforts by the individual to improve their ability to perform at a higher level and become more productive. The increased sense of autonomy the individual experiences, in linking the insight they gain to the actions and behavior changes they make, greatly enhances their engagement with their role as well as their career prospects within the company. Workforce reputation management takes the wide range of disparate data about the workforce being produced across various social media platforms and transforms it into accessible, relevant, and actionable information that helps the organization achieve its desired business objectives. Social media holds untapped insights about your talent, brand and business, and workforce reputation management can help unlock them. Imagine - if you could find the hidden secrets of your businesses, how much more productive and efficient would your organization be? Mark Bennett is a Director of Product Strategy at Oracle. Mark focuses on setting the strategic vision and direction for tools that help organizations understand, shape, and leverage the capabilities of their workforce to achieve business objectives, as well as help individuals work effectively to achieve their goals and navigate their own growth. His combination of a deep technical background in software design and development, coupled with a broad knowledge of business challenges and thinking in today’s globalized, rapidly changing, technology accelerated economy, has enabled him to identify and incorporate key innovations that are central to Oracle Fusion’s unique value proposition. Mark has over the course of his career been in charge of the design, development, and strategy of Talent Management products and the design and development of cutting edge software that is better equipped to handle the increasingly complex demands of users while also remaining easy to use. Follow him @mpbennett

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  • With NVD3.js (nv.models.lineWithFocusChart), how do you set specific ticks on X-axis, when x values are dates?

    - by Panagiotis Panagi
    I'm using nv.models.lineWithFocusChart, where I'm showing some hourly measurements. So the x domain is dates. What I need is to show a tick per hour on X axis: 00:00 01:00 02:00 ... 24:00 I've tried everything I could find but nothing works. It seems that its easy to set specific ticks when values are not dates. But can't figure out how to do it for dates. Here's the code that creates the graph, if it can help: nv.addGraph -> chart = nv.models.lineWithFocusChart(view) chart.yAxis.tickFormat(d3.format(".02f")) d3.select(graphSelector).datum([]).transition().duration(500).call(chart) nv.utils.windowResize -> d3.select(graphSelector).call(chart) chart.xAxis.tickFormat (d) -> d3.time.format(ticksFormat)(new Date(d)) chart.x2Axis.tickFormat (d) -> d3.time.format(ticksFormat)(new Date(d)) chart.xAxis.tickSubdivide(9)

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  • Location.getTime() returning a future time.

    - by fiXedd
    The following code: // get the last known location Criteria c = new Criteria(); c.setAccuracy(Criteria.ACCURACY_FINE); Location lastKnown = mLocationManager.getLastKnownLocation(mLocationManager.getBestProvider(c, true)); // compare times long currentTime = System.currentTimeMillis(); long gpsTime = lastKnown.getTime(); long age = (currentTime - gpsTime) / 1000; Gives me: currentTime = 1270062152738 gpsTime = 1270085378000 age = -23225 If you'll notice, it's returning the last location fix's time as a time in the future. Why is this happening? EDIT: From Location.getTime() : Returns the UTC time of this fix, in milliseconds since January 1, 1970. From System.currentTimeMillis() : Returns the current system time in milliseconds since January 1, 1970 00:00:00 UTC. This method shouldn't be used for measuring timeouts or other elapsed time measurements, as changing the system time can affect the results.

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  • Raspberry Pi cluster, neuron networks and brain simulation

    - by jokoon
    Since the RBPI (Raspberry Pi) has very low power consumption and very low production price, it means one could build a very big cluster with those. I'm not sure, but a cluster of 100000 RBPI would take little power and little room. Now I think it might not be as powerful as existing supercomputers in terms of FLOPS or others sorts of computing measurements, but could it allow better neuronal network simulation ? I'm not sure if saying "1 CPU = 1 neuron" is a reasonable statement, but it seems valid enough. So does it mean such a cluster would more efficient for neuronal network simulation, since it's far more parallel than other classical clusters ?

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  • What can be done to speed up synchronous WCF calls?

    - by Dimitri C.
    My performance measurements of synchronous WCF calls from within a Silverlight application showed I can make 7 calls/s on a localhost connection, which is very slow. Can this be speeded up, or is this normal? This is my test code: const UInt32 nrCalls = 100; ICalculator calculator = new CalculatorClient(); // took over from the MSDN calculator example for (double i = 0; i < nrCalls; ++i) { var call = calculator.BeginSubtract(i + 1, 1, null, null); call.AsyncWaitHandle.WaitOne(); double result = calculator.EndSubtract(call); } Remarks: CPU load is almost 0%. Apparently, the WCF module is waiting for something. I tested this both on Firefox 3.6 and Internet Explorer 7. I'm using Silverlight v3.0

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  • Problem measuring N times the execution time of a code block

    - by Nazgulled
    EDIT: I just found my problem after writing this long post explaining every little detail... If someone can give me a good answer on what I'm doing wrong and how can I get the execution time in seconds (using a float with 5 decimal places or so), I'll mark that as accepted. Hint: The problem was on how I interpreted the clock_getttime() man page. Hi, Let's say I have a function named myOperation that I need to measure the execution time of. To measure it, I'm using clock_gettime() as it was recommend here in one of the comments. My teacher recommends us to measure it N times so we can get an average, standard deviation and median for the final report. He also recommends us to execute myOperation M times instead of just one. If myOperation is a very fast operation, measuring it M times allow us to get a sense of the "real time" it takes; cause the clock being used might not have the required precision to measure such operation. So, execution myOperation only one time or M times really depends if the operation itself takes long enough for the clock precision we are using. I'm having trouble dealing with that M times execution. Increasing M decreases (a lot) the final average value. Which doesn't make sense to me. It's like this, on average you take 3 to 5 seconds to travel from point A to B. But then you go from A to B and back to A 5 times (which makes it 10 times, cause A to B is the same as B to A) and you measure that. Than you divide by 10, the average you get is supposed to be the same average you take traveling from point A to B, which is 3 to 5 seconds. This is what I want my code to do, but it's not working. If I keep increasing the number of times I go from A to B and back A, the average will be lower and lower each time, it makes no sense to me. Enough theory, here's my code: #include <stdio.h> #include <time.h> #define MEASUREMENTS 1 #define OPERATIONS 1 typedef struct timespec TimeClock; TimeClock diffTimeClock(TimeClock start, TimeClock end) { TimeClock aux; if((end.tv_nsec - start.tv_nsec) < 0) { aux.tv_sec = end.tv_sec - start.tv_sec - 1; aux.tv_nsec = 1E9 + end.tv_nsec - start.tv_nsec; } else { aux.tv_sec = end.tv_sec - start.tv_sec; aux.tv_nsec = end.tv_nsec - start.tv_nsec; } return aux; } int main(void) { TimeClock sTime, eTime, dTime; int i, j; for(i = 0; i < MEASUREMENTS; i++) { printf(" » MEASURE %02d\n", i+1); clock_gettime(CLOCK_REALTIME, &sTime); for(j = 0; j < OPERATIONS; j++) { myOperation(); } clock_gettime(CLOCK_REALTIME, &eTime); dTime = diffTimeClock(sTime, eTime); printf(" - NSEC (TOTAL): %ld\n", dTime.tv_nsec); printf(" - NSEC (OP): %ld\n\n", dTime.tv_nsec / OPERATIONS); } return 0; } Notes: The above diffTimeClock function is from this blog post. I replaced my real operation with myOperation() because it doesn't make any sense to post my real functions as I would have to post long blocks of code, you can easily code a myOperation() with whatever you like to compile the code if you wish. As you can see, OPERATIONS = 1 and the results are: » MEASURE 01 - NSEC (TOTAL): 27456580 - NSEC (OP): 27456580 For OPERATIONS = 100 the results are: » MEASURE 01 - NSEC (TOTAL): 218929736 - NSEC (OP): 2189297 For OPERATIONS = 1000 the results are: » MEASURE 01 - NSEC (TOTAL): 862834890 - NSEC (OP): 862834 For OPERATIONS = 10000 the results are: » MEASURE 01 - NSEC (TOTAL): 574133641 - NSEC (OP): 57413 Now, I'm not a math wiz, far from it actually, but this doesn't make any sense to me whatsoever. I've already talked about this with a friend that's on this project with me and he also can't understand the differences. I don't understand why the value is getting lower and lower when I increase OPERATIONS. The operation itself should take the same time (on average of course, not the exact same time), no matter how many times I execute it. You could tell me that that actually depends on the operation itself, the data being read and that some data could already be in the cache and bla bla, but I don't think that's the problem. In my case, myOperation is reading 5000 lines of text from an CSV file, separating the values by ; and inserting those values into a data structure. For each iteration, I'm destroying the data structure and initializing it again. Now that I think of it, I also that think that there's a problem measuring time with clock_gettime(), maybe I'm not using it right. I mean, look at the last example, where OPERATIONS = 10000. The total time it took was 574133641ns, which would be roughly 0,5s; that's impossible, it took a couple of minutes as I couldn't stand looking at the screen waiting and went to eat something.

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  • Using Inch or cm/mm from metric system for americans and canadians?

    - by gamma
    We're developing an international product that displays a ruler to the user. Now in Germany and many other countries its of course common to use the metric system: cm or mm. I'm aware that americans and canadians (and maybe others too) do still use inches, feet and yards. So the question is: will todays americans (and other inch-country-citizens) understand the metric system and take it for granted - or do they still love their inches so much that they'd rather die than use a product with incorrect measurements? ( sorry for being blunt ;) )

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  • Efficient way to create/unpack large bitfields in C?

    - by drhorrible
    I have one microcontroller sampling from a lot of ADC's, and sending the measurements over a radio at a very low bitrate, and bandwidth is becoming an issue. Right now, each ADC only give us 10 bits of data, and its being stored in a 16-bit integer. Is there an easy way to pack them in a deterministic way so that the first measurement is at bit 0, second at bit 10, third at bit 20, etc? To make matters worse, the microcontroller is little endian, and I have no control over the endianness of the computer on the other side.

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  • NoSQL and meteorological data

    - by christian studer
    So there's this new cool thing, these NoSQL-databases. And so there's my data: Rows of rows of rows of meteorological data: Values, representing certain measurements at a certain station (Identified by a WMO number, not coordinates), at a certain time. Not every station measures every parameter, not every parameter is measured all the time. I store this data (30 years worth of hourly values, resulting in ~1 billion values) currently in MySQL. The continous growth and the forseeable addition of even more data give me a little headache. Reading about the document based NoSQL systems which seem to scale rather easily, I was wondering if NoSQL is a viable data storage concept for meteorological data too. Do you have any experience with this?

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  • How to estimate the thread context switching overhead?

    - by Ignas Limanauskas
    I am trying to improve the performance of the threaded application with real-time deadlines. It is running on Windows Mobile and written in C / C++. I have a suspicion that high frequency of thread switching might be causing tangible overhead, but can neither prove it or disprove it. As everybody knows, lack of proof is not a proof of opposite :). Thus my question is twofold: If exists at all, where can I find any actual measurements of the cost of switching thread context? Without spending time writing a test application, what are the ways to estimate the thread switching overhead in the existing application? Does anyone know a way to find out the number of context switches (on / off) for a given thread?

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