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  • Fastest Algorithm to scale down 32Bit RGB IMAGE.

    - by Sunny
    which algorithm to use to scale down 32Bit RGB IMAGE to custom resolution? Algorithm should average pixels. for example If I have 100x100 image and I want new Image of size 20x50. Avg of first five pixels of first source row will give first pixel of dest, And avg of first two pixels of first source column will give first dest column pixel. Currently what I do is first scale down in X resolution, and after that I scale down in Y resolution. I need one temp buffer in this method. Is there any optimized method that you know?

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  • Does anyone really understand how HFSC scheduling in Linux/BSD works?

    - by Mecki
    I read the original SIGCOMM '97 PostScript paper about HFSC, it is very technically, but I understand the basic concept. Instead of giving a linear service curve (as with pretty much every other scheduling algorithm), you can specify a convex or concave service curve and thus it is possible to decouple bandwidth and delay. However, even though this paper mentions to kind of scheduling algorithms being used (real-time and link-share), it always only mentions ONE curve per scheduling class (the decoupling is done by specifying this curve, only one curve is needed for that). Now HFSC has been implemented for BSD (OpenBSD, FreeBSD, etc.) using the ALTQ scheduling framework and it has been implemented Linux using the TC scheduling framework (part of iproute2). Both implementations added two additional service curves, that were NOT in the original paper! A real-time service curve and an upper-limit service curve. Again, please note that the original paper mentions two scheduling algorithms (real-time and link-share), but in that paper both work with one single service curve. There never have been two independent service curves for either one as you currently find in BSD and Linux. Even worse, some version of ALTQ seems to add an additional queue priority to HSFC (there is no such thing as priority in the original paper either). I found several BSD HowTo's mentioning this priority setting (even though the man page of the latest ALTQ release knows no such parameter for HSFC, so officially it does not even exist). This all makes the HFSC scheduling even more complex than the algorithm described in the original paper and there are tons of tutorials on the Internet that often contradict each other, one claiming the opposite of the other one. This is probably the main reason why nobody really seems to understand how HFSC scheduling really works. Before I can ask my questions, we need a sample setup of some kind. I'll use a very simple one as seen in the image below: Here are some questions I cannot answer because the tutorials contradict each other: What for do I need a real-time curve at all? Assuming A1, A2, B1, B2 are all 128 kbit/s link-share (no real-time curve for either one), then each of those will get 128 kbit/s if the root has 512 kbit/s to distribute (and A and B are both 256 kbit/s of course), right? Why would I additionally give A1 and B1 a real-time curve with 128 kbit/s? What would this be good for? To give those two a higher priority? According to original paper I can give them a higher priority by using a curve, that's what HFSC is all about after all. By giving both classes a curve of [256kbit/s 20ms 128kbit/s] both have twice the priority than A2 and B2 automatically (still only getting 128 kbit/s on average) Does the real-time bandwidth count towards the link-share bandwidth? E.g. if A1 and B1 both only have 64kbit/s real-time and 64kbit/s link-share bandwidth, does that mean once they are served 64kbit/s via real-time, their link-share requirement is satisfied as well (they might get excess bandwidth, but lets ignore that for a second) or does that mean they get another 64 kbit/s via link-share? So does each class has a bandwidth "requirement" of real-time plus link-share? Or does a class only have a higher requirement than the real-time curve if the link-share curve is higher than the real-time curve (current link-share requirement equals specified link-share requirement minus real-time bandwidth already provided to this class)? Is upper limit curve applied to real-time as well, only to link-share, or maybe to both? Some tutorials say one way, some say the other way. Some even claim upper-limit is the maximum for real-time bandwidth + link-share bandwidth? What is the truth? Assuming A2 and B2 are both 128 kbit/s, does it make any difference if A1 and B1 are 128 kbit/s link-share only, or 64 kbit/s real-time and 128 kbit/s link-share, and if so, what difference? If I use the seperate real-time curve to increase priorities of classes, why would I need "curves" at all? Why is not real-time a flat value and link-share also a flat value? Why are both curves? The need for curves is clear in the original paper, because there is only one attribute of that kind per class. But now, having three attributes (real-time, link-share, and upper-limit) what for do I still need curves on each one? Why would I want the curves shape (not average bandwidth, but their slopes) to be different for real-time and link-share traffic? According to the little documentation available, real-time curve values are totally ignored for inner classes (class A and B), they are only applied to leaf classes (A1, A2, B1, B2). If that is true, why does the ALTQ HFSC sample configuration (search for 3.3 Sample configuration) set real-time curves on inner classes and claims that those set the guaranteed rate of those inner classes? Isn't that completely pointless? (note: pshare sets the link-share curve in ALTQ and grate the real-time curve; you can see this in the paragraph above the sample configuration). Some tutorials say the sum of all real-time curves may not be higher than 80% of the line speed, others say it must not be higher than 70% of the line speed. Which one is right or are they maybe both wrong? One tutorial said you shall forget all the theory. No matter how things really work (schedulers and bandwidth distribution), imagine the three curves according to the following "simplified mind model": real-time is the guaranteed bandwidth that this class will always get. link-share is the bandwidth that this class wants to become fully satisfied, but satisfaction cannot be guaranteed. In case there is excess bandwidth, the class might even get offered more bandwidth than necessary to become satisfied, but it may never use more than upper-limit says. For all this to work, the sum of all real-time bandwidths may not be above xx% of the line speed (see question above, the percentage varies). Question: Is this more or less accurate or a total misunderstanding of HSFC? And if assumption above is really accurate, where is prioritization in that model? E.g. every class might have a real-time bandwidth (guaranteed), a link-share bandwidth (not guaranteed) and an maybe an upper-limit, but still some classes have higher priority needs than other classes. In that case I must still prioritize somehow, even among real-time traffic of those classes. Would I prioritize by the slope of the curves? And if so, which curve? The real-time curve? The link-share curve? The upper-limit curve? All of them? Would I give all of them the same slope or each a different one and how to find out the right slope? I still haven't lost hope that there exists at least a hand full of people in this world that really understood HFSC and are able to answer all these questions accurately. And doing so without contradicting each other in the answers would be really nice ;-)

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  • using Excel VBA, given the daily price of 50 stocks, choose 10 stocks such that they have the minumu

    - by correl
    The high-level goal is to choose 10 stocks that have the lowest correlation among one another, out of a pool of 50, so that I can have a well-diversified portfolio. I have managed to write some VBA macro to download the past 3 years of daily price data from Yahoo finance, and then compute the 50x50 correlation matrix (using the Correl function), using the daily close as the data. What I have tried so far is just some local-maximum heuristic: - For the two stocks that have the highest correlation with each other, remove one of them. Between the two, remove the one that has the higher average correlation with all the other stocks. - When I remove a stock from the pool, I just delete the correponding row and column, to give a smaller matrix. - Repeat until I have just 10 stocks remaining (a 10x10 matrix). I was wondering if there is some algorithm that already solves such a problem and gives the optimum solution?

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  • Building v8 without JIT

    - by rames
    Hello, I would like to run some tests on v8 with and without JIT to compare performances. I know JIT will improve my average speed performance, but it would be nice for me to have some actual more detailed tests results as I want to work with mobile platforms. I haven't found how to enable or disable JIT like it exists on Squirrelfish (cf. ENABLE_JIT in JavaScriptCore/wtf/Platform.h). Does somebody knows how to do that with v8? Thanks. Alexandre

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  • SumProduct over sets of cells (not contiguous)

    - by Craig
    I have a total data set that is for 4 different groupings. One of the values is the average time, the other is count. For the Total I have to multiply these and then divide by the total of the count. Currently I use: =SUM(D32*D2,D94*D64,D156*D126,D218*D188)/SUM(D32,D94,D156,D218) I would rather use a SumProduct if I can to make it more readable. I tried to do: =SUMPRODUCT((D2,D64,D126,D188),(D32,D94,D156,D218))/SUM(D32,94,D156,D218) But as you can tell by my posting here, that did not work. Is there a way to do SumProduct like I want? Thoughts, Answers, Questions, Comments? Craig

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  • jQuery Star Rating plugin - select in callback causes infinite loop

    - by Ian
    Using the jQuery Star Rating plugin everything works well until I select a star rating from the rating's callback handler. Simple example: $('.rating').rating({ ... callback: function(value){ $.ajax({ type: "POST", url: ... data: {rating: value}, success: function(data){ $('.rating').rating('select', 1); } }); } }); I'm guessing this infinite loop occurs because the callback is fired after a manual 'select' as well. Once a user submits their rating I'd like to 'select' the average rating across all users (this value is in data returned to the success handler). How can I do this without triggering an infinite loop?

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  • Getting AveragePower and PeakPower for a Channel in AVAudioRecorder

    - by Biranchi
    Hi all, I am annoyed with this piece of code. I am trying to get the averagePowerForChannel and peakPowerForChannel while recording Audio, but every time i am getting it as 0.0 Below is my code for recording audio : NSMutableDictionary *recordSetting =[[NSDictionary alloc] initWithObjectsAndKeys:[NSNumber numberWithFloat: 22050.0], AVSampleRateKey, [NSNumber numberWithInt: kAudioFormatLinearPCM], AVFormatIDKey, [NSNumber numberWithInt: 1], AVNumberOfChannelsKey, [NSNumber numberWithInt: AVAudioQualityMax], AVEncoderAudioQualityKey, [NSNumber numberWithInt:32],AVLinearPCMBitDepthKey, [NSNumber numberWithBool:NO],AVLinearPCMIsBigEndianKey, [NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey, nil]; recorder1 = [[AVAudioRecorder alloc] initWithURL:[NSURL fileURLWithPath:audioFilePath] settings:recordSetting error:&err]; recorder1.meteringEnabled = YES; recorder1.delegate=self; [recorder1 prepareToRecord]; [recorder1 record]; levelTimer = [NSTimer scheduledTimerWithTimeInterval: 0.3f target: self selector: @selector(levelTimerCallback:) userInfo: nil repeats: YES]; - (void)levelTimerCallback:(NSTimer *)timer { [recorder1 updateMeters]; NSLog(@"Peak Power : %f , %f", [recorder1 peakPowerForChannel:0], [recorder1 peakPowerForChannel:1]); NSLog(@"Average Power : %f , %f", [recorder1 averagePowerForChannel:0], [recorder1 averagePowerForChannel:1]); } What is the error in the code ???

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  • Metaprograming - self explanatory code - tutorials, articles, books

    - by elena
    Hello everybody, I am looking into improving my programming skils (actually I try to do my best to suck less each year, as our Jeff Atwood put it), so I was thinking into reading stuff about metaprogramming and self explanatory code. I am looking for something like an idiot's guide to this (free books for download, online resources). Also I want more than your average wiki page and also something language agnostic or preferably with Java examples. Do you know of such resources that will allow to efficiently put all of it into prectice (I know experience has a lot to say in all of this but i kind of want to build experience avoiding the flow bad decitions - experience - good decitions)? Thank you!

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  • How to implement SCORM in Objective C

    - by iranjan
    Hey, Do you know how to implement SCORM (Sharable Content Object Reference Model) in Objective C for eLearning content? Let me explain you what exactly I am looking for. I have one MCQ (multiple choice question) application which has 4 questions. On attempting each question I want my application to interact with a SCORM compatible server with result (whether the user has attempted correct one or not). The communication channel should be to and fro. May be at the end of the MCQ I want to show result which will come from the server with some calculations*(like Score : 85% number of attempts : 16 average score:16.7% etc.)*. How should I go about it? Please guide if you have already achieved it regards Ranjan.

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  • Extract Email Attachments from Outlook (exchange server) using C#

    - by ChokkaMedex
    Extract Email Attachments from Outlook (exchange server) using C# I need to run a script or Service - Which can automatically deduct the attachment file from a Specific Email Id ( [email protected]). Attachment file will be .zip format. I need to Unzip this file.. I need to do this task completely in an automated format. On an average, I will receive only one email in a week. I need to write the program in C#.Net...! Kindly help me by sharing your logics ... Many thanks in advance..!

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  • Algorithm to determine thread "hotness"

    - by nickf
    I'm trying to come up with a way to determine how "hot" certain threads are in a forum. What criteria would you use and why? How would these come together to give a hotness score? The criteria I'm thinking of include: how many replies how long since the last reply average time between replies The problems this algorithm must solve: A thread which has 500 replies is clearly hot, unless the last reply was over a year ago. A thread with 500 replies that was replied to a second ago is clearly hot, unless it's taken 4 years to reach 500 replies. A thread with 15 replies in the last 4 minutes is really hot! Any ideas, thoughts or complete solutions out there?

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  • How to extract frequency information from samples from PortAudio using FFTW in C

    - by houbysoft
    Hi all, I want to make a program that would record audio data using PortAudio (I have this part done) and then display the frequency information of that recorded audio (for now, I'd like to display the average frequency of each of the group of samples as they come in). From some research I've done, I know that I need to do an FFT. So I googled for a library to do that, in C, and found FFTW. However, now I am a little lost. What exactly am I supposed to do with the samples I recorded to extract some frequency information from them? What kind of FFT should I use (I assume I'd need a real data 1D?)? And once I'd do the FFT, how do I get the frequency information from the data it gives me? Thanks a lot in advance.

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  • What's the right way to calculate derived data in a Flex AdvancedDataGrid using summaries?

    - by Chris R
    Here's the gist of the problem: I have a set of rows of data with (say) field1 to field4 in them. I'm using a GroupingCollection to group on field1 and field2. So, I have something like this: f1.1 f2.1 f3.1 f4.1 f3.2 f4.2 f2.2 f3.3 f4.3 f3.4 f4.4 f3.5 f4.5 f1.2 f2.1 f3.6 f4.6 f2.2 f3.7 f4.7 f3.8 f4.8 f3.9 f4.9 (or at least, I hope that's clear enough) I need to calculate some derived values for each leaf row, for example f3, that is the ratio of f3 to the average of all f3 in that particular part of the tree. So, for f3.7 I need to calculate f3.7 / avg(f3.7..f3.9) and fill that into the f3_index property on the row, displaying that in lieu of f3 itself. So, basically, what it looks like I have to do is add source field values in the summarizeFunction implementation. It seems to me that there must be a better way of doing this. Is there?

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  • why cacti is showing empty graph.??.even if rrd file created..

    - by Divya mohan Singh
    hii, i have develop my own snmp service..and i want to plot a graph of an OID provided. so, i have create graph in cacti. -) Its is showing device up. -) It is creating rrd file.(RRDTool says OK). -) showing the graph but its empty. but when i check it say rrdtool fetch AVERAGE it showing me all the values nan only..the monitored OID is having value 47 and i have set min=0 and max=100 i am using cacti appliance by rpath http://www.rpath.org/ui/#/appliances?id=http://www.rpath.org/api/products/cacti-appliance still i can show value on graph.. where is the problem??can anyone plz tell me??

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  • Slow insert speed in Postgresql memory tablespace

    - by Prashant
    Hi, I have a requirement where I need to store the records at rate of 10,000 records/sec into a database (with indexing on a few fields). Number of columns in one record is 25. I am doing a batch insert of 100,000 records in one transaction block. To improve the insertion rate, I changed the tablespace from disk to RAM.With that I am able to achieve only 5,000 inserts per second. I have also done the following tuning in the postgres config: Indexes : no fsync : false logging : disabled Other information: - Tablespace : RAM - Number of columns in one row : 25 (mostly integers) - CPU : 4 core, 2.5 GHz - RAM : 48 GB I am wondering why a single insert query is taking around 0.2 msec on average when database is not writing anything on disk (as I am using RAM based tablespace). Is there something I am doing wrong? Help appreciated. Prashant

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  • zlib memory usage / performance. With 500kb of data.

    - by unixman83
    Is zLib Worth it? Are there other better suited compressors? I am using an embedded system. Frequently, I have only 3MB of RAM or less available to my application. So I am considering using zlib to compress my buffers. I am concerned about overhead however. The buffer's average size will be 30kb. This probably won't get compressed by zlib. Anyone know of a good compressor for extremely limited memory environments? However, I will experience occasional maximum buffer sizes of 700kb, with 500kb much more common. Is zlib worth it in this case? Or is the overhead too much to justify? My sole considerations for compression are RAM overhead of algorithm and performance at least as good as zlib.

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  • How do I regenerate statistics in Openx?

    - by Martin Bauer
    ue to faulty hardware, statistics generated over a 2 week period were significantly higher than normal (10000 times higher than normal). After moving the application to a new server, the problem rectified itself. The issue I have is that there are 2 weeks of stats that are clearly wrong. I have checked the raw impressions table for the affected fortnight and it seems to be correct (ie. stats per banner per day match the average for the previous month). Looking at the intermediate & summary impressions tables, the values are inflated. I understand from the openx forum (http://forum.openx.org/index.php?s=7796fd9dae40e020a010773746f3ada9&showtopic=503424297) it's possible to regenerate stats from the raw data but it will only regenerate stats per hour, meaning regenerating stats for 2 weeks would be very time consuming. Is there another, more efficient way to regenerate the stats from the raw data for the affected fortnight?

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  • Starting a Blog using Microsoft.Net technologies

    - by manav inder
    I want to start a blog using Microsoft technologies. My primary reason is to get more in-sync with technologies which are very much in demand. It does not matter how steep is the learning curve as long I am willing to devote all the time in the world. There are lot going on like Microsoft WebAPI, Dot net nuke MVC SPA etc. Let me tell you what i know I have very good experience in developing database driven .net application using winforms and wpf. Average experience in asp.net and asp.net mvc. Good in entity framework, ado.net and wcf rest services. Good in IoC/DI.

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  • Entity Framework and Sql Server view question

    - by Sergio Romero
    Hi to all, For several reasons that I don't have the liberty to talk about, we are defining a view on our Sql Server 2005 database like so: CREATE VIEW [dbo].[MeterProvingStatisticsPoint] AS SELECT CAST(0 AS BIGINT) AS 'RowNumber', CAST(0 AS BIGINT) AS 'ProverTicketId', CAST(0 AS INT) AS 'ReportNumber', GETDATE() AS 'CompletedDateTime', CAST(1.1 AS float) AS 'MeterFactor', CAST(1.1 AS float) AS 'Density', CAST(1.1 AS float) AS 'FlowRate', CAST(1.1 AS float) AS 'Average', CAST(1.1 AS float) AS 'StandardDeviation', CAST(1.1 AS float) AS 'MeanPlus2XStandardDeviation', CAST(1.1 AS float) AS 'MeanMinus2XStandardDeviation' WHERE 0 = 1 The idea is that the Entity Framework will create an entity based on this query, which it does, but it generates it with an error that states the following: "warning 6002: The table/view 'Keystone_Local.dbo.MeterProvingStatisticsPoint' does not have a primary key defined. The key has been inferred and the definition was created as a read-only table/view." And it decides that the CompletedDateTime field will be this entity primary key. We are using EdmGen to generate the model. Is there a way not to have the entity framework include any field of this view as a primary key? Thanks for help.

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  • How do I make "simple" throughput servlet-filter?

    - by Tommy
    I'm looking to create a filter that can give me two things: number of request pr minute, and average responsetime pr minute. I already got the individual readings, I'm just not sure how to add them up. My filter captures every request, and it records the time each request takes: public void doFilter(ServletRequest request, ...() { long start = System.currentTimeMillis(); chain.doFilter(request, response); long stop = System.currentTimeMillis(); String time = Util.getTimeDifferenceInSec(start, stop); } This information will be used to create some pretty Google Chart charts. I don't want to store the data in any database. Just a way to get current numbers out when requested As this is a high volume application; low overhead is essential. I'm assuming my applicationserver doesn't provide this information.

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  • Does anyone really understand how HFSC scheduling in Linux/BSD works?

    - by Mecki
    I read the original SIGCOMM '97 PostScript paper about HFSC, it is very technically, but I understand the basic concept. Instead of giving a linear service curve (as with pretty much every other scheduling algorithm), you can specify a convex or concave service curve and thus it is possible to decouple bandwidth and delay. However, even though this paper mentions to kind of scheduling algorithms being used (real-time and link-share), it always only mentions ONE curve per scheduling class (the decoupling is done by specifying this curve, only one curve is needed for that). Now HFSC has been implemented for BSD (OpenBSD, FreeBSD, etc.) using the ALTQ scheduling framework and it has been implemented Linux using the TC scheduling framework (part of iproute2). Both implementations added two additional service curves, that were NOT in the original paper! A real-time service curve and an upper-limit service curve. Again, please note that the original paper mentions two scheduling algorithms (real-time and link-share), but in that paper both work with one single service curve. There never have been two independent service curves for either one as you currently find in BSD and Linux. Even worse, some version of ALTQ seems to add an additional queue priority to HSFC (there is no such thing as priority in the original paper either). I found several BSD HowTo's mentioning this priority setting (even though the man page of the latest ALTQ release knows no such parameter for HSFC, so officially it does not even exist). This all makes the HFSC scheduling even more complex than the algorithm described in the original paper and there are tons of tutorials on the Internet that often contradict each other, one claiming the opposite of the other one. This is probably the main reason why nobody really seems to understand how HFSC scheduling really works. Before I can ask my questions, we need a sample setup of some kind. I'll use a very simple one as seen in the image below: Here are some questions I cannot answer because the tutorials contradict each other: What for do I need a real-time curve at all? Assuming A1, A2, B1, B2 are all 128 kbit/s link-share (no real-time curve for either one), then each of those will get 128 kbit/s if the root has 512 kbit/s to distribute (and A and B are both 256 kbit/s of course), right? Why would I additionally give A1 and B1 a real-time curve with 128 kbit/s? What would this be good for? To give those two a higher priority? According to original paper I can give them a higher priority by using a curve, that's what HFSC is all about after all. By giving both classes a curve of [256kbit/s 20ms 128kbit/s] both have twice the priority than A2 and B2 automatically (still only getting 128 kbit/s on average) Does the real-time bandwidth count towards the link-share bandwidth? E.g. if A1 and B1 both only have 64kbit/s real-time and 64kbit/s link-share bandwidth, does that mean once they are served 64kbit/s via real-time, their link-share requirement is satisfied as well (they might get excess bandwidth, but lets ignore that for a second) or does that mean they get another 64 kbit/s via link-share? So does each class has a bandwidth "requirement" of real-time plus link-share? Or does a class only have a higher requirement than the real-time curve if the link-share curve is higher than the real-time curve (current link-share requirement equals specified link-share requirement minus real-time bandwidth already provided to this class)? Is upper limit curve applied to real-time as well, only to link-share, or maybe to both? Some tutorials say one way, some say the other way. Some even claim upper-limit is the maximum for real-time bandwidth + link-share bandwidth? What is the truth? Assuming A2 and B2 are both 128 kbit/s, does it make any difference if A1 and B1 are 128 kbit/s link-share only, or 64 kbit/s real-time and 128 kbit/s link-share, and if so, what difference? If I use the seperate real-time curve to increase priorities of classes, why would I need "curves" at all? Why is not real-time a flat value and link-share also a flat value? Why are both curves? The need for curves is clear in the original paper, because there is only one attribute of that kind per class. But now, having three attributes (real-time, link-share, and upper-limit) what for do I still need curves on each one? Why would I want the curves shape (not average bandwidth, but their slopes) to be different for real-time and link-share traffic? According to the little documentation available, real-time curve values are totally ignored for inner classes (class A and B), they are only applied to leaf classes (A1, A2, B1, B2). If that is true, why does the ALTQ HFSC sample configuration (search for 3.3 Sample configuration) set real-time curves on inner classes and claims that those set the guaranteed rate of those inner classes? Isn't that completely pointless? (note: pshare sets the link-share curve in ALTQ and grate the real-time curve; you can see this in the paragraph above the sample configuration). Some tutorials say the sum of all real-time curves may not be higher than 80% of the line speed, others say it must not be higher than 70% of the line speed. Which one is right or are they maybe both wrong? One tutorial said you shall forget all the theory. No matter how things really work (schedulers and bandwidth distribution), imagine the three curves according to the following "simplified mind model": real-time is the guaranteed bandwidth that this class will always get. link-share is the bandwidth that this class wants to become fully satisfied, but satisfaction cannot be guaranteed. In case there is excess bandwidth, the class might even get offered more bandwidth than necessary to become satisfied, but it may never use more than upper-limit says. For all this to work, the sum of all real-time bandwidths may not be above xx% of the line speed (see question above, the percentage varies). Question: Is this more or less accurate or a total misunderstanding of HSFC? And if assumption above is really accurate, where is prioritization in that model? E.g. every class might have a real-time bandwidth (guaranteed), a link-share bandwidth (not guaranteed) and an maybe an upper-limit, but still some classes have higher priority needs than other classes. In that case I must still prioritize somehow, even among real-time traffic of those classes. Would I prioritize by the slope of the curves? And if so, which curve? The real-time curve? The link-share curve? The upper-limit curve? All of them? Would I give all of them the same slope or each a different one and how to find out the right slope? I still haven't lost hope that there exists at least a hand full of people in this world that really understood HFSC and are able to answer all these questions accurately. And doing so without contradicting each other in the answers would be really nice ;-)

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  • Strange Recurrent Excessive I/O Wait

    - by Chris
    I know quite well that I/O wait has been discussed multiple times on this site, but all the other topics seem to cover constant I/O latency, while the I/O problem we need to solve on our server occurs at irregular (short) intervals, but is ever-present with massive spikes of up to 20k ms a-wait and service times of 2 seconds. The disk affected is /dev/sdb (Seagate Barracuda, for details see below). A typical iostat -x output would at times look like this, which is an extreme sample but by no means rare: iostat (Oct 6, 2013) tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 16.00 0.00 156.00 9.75 21.89 288.12 36.00 57.60 5.50 0.00 44.00 8.00 48.79 2194.18 181.82 100.00 2.00 0.00 16.00 8.00 46.49 3397.00 500.00 100.00 4.50 0.00 40.00 8.89 43.73 5581.78 222.22 100.00 14.50 0.00 148.00 10.21 13.76 5909.24 68.97 100.00 1.50 0.00 12.00 8.00 8.57 7150.67 666.67 100.00 0.50 0.00 4.00 8.00 6.31 10168.00 2000.00 100.00 2.00 0.00 16.00 8.00 5.27 11001.00 500.00 100.00 0.50 0.00 4.00 8.00 2.96 17080.00 2000.00 100.00 34.00 0.00 1324.00 9.88 1.32 137.84 4.45 59.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 22.00 44.00 204.00 11.27 0.01 0.27 0.27 0.60 Let me provide you with some more information regarding the hardware. It's a Dell 1950 III box with Debian as OS where uname -a reports the following: Linux xx 2.6.32-5-amd64 #1 SMP Fri Feb 15 15:39:52 UTC 2013 x86_64 GNU/Linux The machine is a dedicated server that hosts an online game without any databases or I/O heavy applications running. The core application consumes about 0.8 of the 8 GBytes RAM, and the average CPU load is relatively low. The game itself, however, reacts rather sensitive towards I/O latency and thus our players experience massive ingame lag, which we would like to address as soon as possible. iostat: avg-cpu: %user %nice %system %iowait %steal %idle 1.77 0.01 1.05 1.59 0.00 95.58 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sdb 13.16 25.42 135.12 504701011 2682640656 sda 1.52 0.74 20.63 14644533 409684488 Uptime is: 19:26:26 up 229 days, 17:26, 4 users, load average: 0.36, 0.37, 0.32 Harddisk controller: 01:00.0 RAID bus controller: LSI Logic / Symbios Logic MegaRAID SAS 1078 (rev 04) Harddisks: Array 1, RAID-1, 2x Seagate Cheetah 15K.5 73 GB SAS Array 2, RAID-1, 2x Seagate ST3500620SS Barracuda ES.2 500GB 16MB 7200RPM SAS Partition information from df: Filesystem 1K-blocks Used Available Use% Mounted on /dev/sdb1 480191156 30715200 425083668 7% /home /dev/sda2 7692908 437436 6864692 6% / /dev/sda5 15377820 1398916 13197748 10% /usr /dev/sda6 39159724 19158340 18012140 52% /var Some more data samples generated with iostat -dx sdb 1 (Oct 11, 2013) Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util sdb 0.00 15.00 0.00 70.00 0.00 656.00 9.37 4.50 1.83 4.80 33.60 sdb 0.00 0.00 0.00 2.00 0.00 16.00 8.00 12.00 836.00 500.00 100.00 sdb 0.00 0.00 0.00 3.00 0.00 32.00 10.67 9.96 1990.67 333.33 100.00 sdb 0.00 0.00 0.00 4.00 0.00 40.00 10.00 6.96 3075.00 250.00 100.00 sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.00 0.00 0.00 100.00 sdb 0.00 0.00 0.00 2.00 0.00 16.00 8.00 2.62 4648.00 500.00 100.00 sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.00 0.00 0.00 100.00 sdb 0.00 0.00 0.00 1.00 0.00 16.00 16.00 1.69 7024.00 1000.00 100.00 sdb 0.00 74.00 0.00 124.00 0.00 1584.00 12.77 1.09 67.94 6.94 86.00 Characteristic charts generated with rrdtool can be found here: iostat plot 1, 24 min interval: http://imageshack.us/photo/my-images/600/yqm3.png/ iostat plot 2, 120 min interval: http://imageshack.us/photo/my-images/407/griw.png/ As we have a rather large cache of 5.5 GBytes, we thought it might be a good idea to test if the I/O wait spikes would perhaps be caused by cache miss events. Therefore, we did a sync and then this to flush the cache and buffers: echo 3 > /proc/sys/vm/drop_caches and directly afterwards the I/O wait and service times virtually went through the roof, and everything on the machine felt like slow motion. During the next few hours the latency recovered and everything was as before - small to medium lags in short, unpredictable intervals. Now my question is: does anybody have any idea what might cause this annoying behaviour? Is it the first indication of the disk array or the raid controller dying, or something that can be easily mended by rebooting? (At the moment we're very reluctant to do this, however, because we're afraid that the disks might not come back up again.) Any help is greatly appreciated. Thanks in advance, Chris. Edited to add: we do see one or two processes go to 'D' state in top, one of which seems to be kjournald rather frequently. If I'm not mistaken, however, this does not indicate the processes causing the latency, but rather those affected by it - correct me if I'm wrong. Does the information about uninterruptibly sleeping processes help us in any way to address the problem? @Andy Shinn requested smartctl data, here it is: smartctl -a -d megaraid,2 /dev/sdb yields: smartctl 5.40 2010-07-12 r3124 [x86_64-unknown-linux-gnu] (local build) Copyright (C) 2002-10 by Bruce Allen, http://smartmontools.sourceforge.net Device: SEAGATE ST3500620SS Version: MS05 Serial number: Device type: disk Transport protocol: SAS Local Time is: Mon Oct 14 20:37:13 2013 CEST Device supports SMART and is Enabled Temperature Warning Disabled or Not Supported SMART Health Status: OK Current Drive Temperature: 20 C Drive Trip Temperature: 68 C Elements in grown defect list: 0 Vendor (Seagate) cache information Blocks sent to initiator = 1236631092 Blocks received from initiator = 1097862364 Blocks read from cache and sent to initiator = 1383620256 Number of read and write commands whose size <= segment size = 531295338 Number of read and write commands whose size > segment size = 51986460 Vendor (Seagate/Hitachi) factory information number of hours powered up = 36556.93 number of minutes until next internal SMART test = 32 Error counter log: Errors Corrected by Total Correction Gigabytes Total ECC rereads/ errors algorithm processed uncorrected fast | delayed rewrites corrected invocations [10^9 bytes] errors read: 509271032 47 0 509271079 509271079 20981.423 0 write: 0 0 0 0 0 5022.039 0 verify: 1870931090 196 0 1870931286 1870931286 100558.708 0 Non-medium error count: 0 SMART Self-test log Num Test Status segment LifeTime LBA_first_err [SK ASC ASQ] Description number (hours) # 1 Background short Completed 16 36538 - [- - -] # 2 Background short Completed 16 36514 - [- - -] # 3 Background short Completed 16 36490 - [- - -] # 4 Background short Completed 16 36466 - [- - -] # 5 Background short Completed 16 36442 - [- - -] # 6 Background long Completed 16 36420 - [- - -] # 7 Background short Completed 16 36394 - [- - -] # 8 Background short Completed 16 36370 - [- - -] # 9 Background long Completed 16 36364 - [- - -] #10 Background short Completed 16 36361 - [- - -] #11 Background long Completed 16 2 - [- - -] #12 Background short Completed 16 0 - [- - -] Long (extended) Self Test duration: 6798 seconds [113.3 minutes] smartctl -a -d megaraid,3 /dev/sdb yields: smartctl 5.40 2010-07-12 r3124 [x86_64-unknown-linux-gnu] (local build) Copyright (C) 2002-10 by Bruce Allen, http://smartmontools.sourceforge.net Device: SEAGATE ST3500620SS Version: MS05 Serial number: Device type: disk Transport protocol: SAS Local Time is: Mon Oct 14 20:37:26 2013 CEST Device supports SMART and is Enabled Temperature Warning Disabled or Not Supported SMART Health Status: OK Current Drive Temperature: 19 C Drive Trip Temperature: 68 C Elements in grown defect list: 0 Vendor (Seagate) cache information Blocks sent to initiator = 288745640 Blocks received from initiator = 1097848399 Blocks read from cache and sent to initiator = 1304149705 Number of read and write commands whose size <= segment size = 527414694 Number of read and write commands whose size > segment size = 51986460 Vendor (Seagate/Hitachi) factory information number of hours powered up = 36596.83 number of minutes until next internal SMART test = 28 Error counter log: Errors Corrected by Total Correction Gigabytes Total ECC rereads/ errors algorithm processed uncorrected fast | delayed rewrites corrected invocations [10^9 bytes] errors read: 610862490 44 0 610862534 610862534 20470.133 0 write: 0 0 0 0 0 5022.480 0 verify: 2861227413 203 0 2861227616 2861227616 100872.443 0 Non-medium error count: 1 SMART Self-test log Num Test Status segment LifeTime LBA_first_err [SK ASC ASQ] Description number (hours) # 1 Background short Completed 16 36580 - [- - -] # 2 Background short Completed 16 36556 - [- - -] # 3 Background short Completed 16 36532 - [- - -] # 4 Background short Completed 16 36508 - [- - -] # 5 Background short Completed 16 36484 - [- - -] # 6 Background long Completed 16 36462 - [- - -] # 7 Background short Completed 16 36436 - [- - -] # 8 Background short Completed 16 36412 - [- - -] # 9 Background long Completed 16 36404 - [- - -] #10 Background short Completed 16 36401 - [- - -] #11 Background long Completed 16 2 - [- - -] #12 Background short Completed 16 0 - [- - -] Long (extended) Self Test duration: 6798 seconds [113.3 minutes]

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  • WCF - Network Cost

    - by Mubashar Ahmad
    Dear Devs I have a wcf service deployed on IIS with basicHttpBinding and aspNetCompatibilityEnabled=true I have a test client as well which invokes multiple service functions simultaneously. To check the performance of service call on client and server I calculated the Avg time it takes to complete a service request on client(in proxy code) and on server as well. after a test of 8 hrs (server and client were on the same machine) i came to know that average response time on client is around 34ms where as the Avg execution time on server is around 3ms so the difference is 31ms. I would like to know why every call is taking 31ms is it justified? and how can i reduce this?

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  • Looking for SQL Server Performance Monitor Tools

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    I may be approaching this problem from the wrong angle but what I'm thinking of is some kind of performance monitor tool for SQl server that works in a similar way to code performance tools, e.g. I;d like to see an output of how many times each stored procedure was called, average executuion time and possibly various resource usage stats such as cache/index utilisation, resultign disk access and table scans, etc. As far as I can tell the performance monitor that comes with SQL Server just logs the various calls but doesn't report he variosu stats I'm looking for. Potentially I just need a tool to analyze the log output?

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  • jQuery/Javascript framework efficiency

    - by Russell
    My latest project is using a javascript framework (jQuery), along with some plugins (validation, jquery-ui, datepicker, facebox, ...) to help make a modern web application. I am now finding pages loading slower than I am used to. After some js profiling (thanks VS2010!), it seems a lot of the time is taken procesing inside the framework. Now I understand the more complex the ui tools, the more processing needs to be done. The project is not yet at a large stage and I think would be average functions. At this stage I can see it is not going to scale well. I noticed things like the 'each' command in jQuery takes quite a lot of processing time. Have others experienced some extra latency using JS frameworks? How do I minimise their effect on page performance? Are there best practices on implementation using JS frameworks? Thanks

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