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  • use of tcp_delack_min on redhat linux (kernel 2.6.18)

    - by user41466
    Hello, we're moving from Solaris to Redhat Linux, and trying to duplicate our low-latency setup, that, on solaris, includes the ndd settings related to TCP NO DELAY, and NAGLE ALGORITHM. I got the impression that those parameters are not all configurable system-wide, but still found some info. we have configured our applications to run with no nagle algorithm, but that is not sufficient. we have found an interesting RH article talking presenting the tcp_delack_min parameter, however, when browsing /proc/sys/net/ipv4/ , I can't find it there. would it be safe to assume that simply "adding" the parameter as it's said on the doc would be enough, or rather that the option is not supported by this version (would be strange, as RH specify that it "can be performed on a standard Red Hat Enterprise Linux installation") ? any other idea / recommendation to improve latency further ? thanks

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  • SSH and Latent Connections (e.g., satellite connections)

    - by user71494
    Most of the week I live in the city where I have a typical broadband connection, but most weekends I'm out of town and only have access to a satellite connection. Trying to work over SSH on a satellite connection, while possible, is hardly desirable due to the high latency ( 1 second). My question is this: Is there any software that will do something like buffering keystrokes on my local machine before they're sent over SSH to help make the lag on individual keystrokes a little bit more transparent? Essentially I'm looking for something that would reduce the effects of the high latency for everything except for commands (e.g., opening files, changing to a new directory, etc.). I've already discovered that vim can open remote files locally and rewrite them remotely, but, while this is a huge help, it is not quite what I'm looking for since it only works when editing files, and requires opening a connection every time a read/write occurs. (For anyone who may not know how to do this and is curious, just use this command: 'vim scp://host/file/path/here)

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  • SSH and Latent Connections (e.g., satellite connections)

    - by user71494
    Most of the week I live in the city where I have a typical broadband connection, but most weekends I'm out of town and only have access to a satellite connection. Trying to work over SSH on a satellite connection, while possible, is hardly desirable due to the high latency ( 1 second). My question is this: Is there any software that will do something like buffering keystrokes on my local machine before they're sent over SSH to help make the lag on individual keystrokes a little bit more transparent? Essentially I'm looking for something that would reduce the effects of the high latency for everything except for commands (e.g., opening files, changing to a new directory, etc.). I've already discovered that vim can open remote files locally and rewrite them remotely, but, while this is a huge help, it is not quite what I'm looking for since it only works when editing files, and requires opening a connection every time a read/write occurs. (For anyone who may not know how to do this and is curious, just use this command: 'vim scp://host/file/path/here)

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  • HiLo: how to control Low values

    - by Sandor Drieënhuizen
    I'm using the HiLo generator in my S#rpArchitecture/NHibernate project and I'm performing a large import batch. I've read somewhere about the possibility to predict the Low values of any new records because they are generated on the client. I figure this means I can control the Low values myself or at least fetch the next Low value from somewhere. The reason I want to use this is that I want to set relations to other entities I'm about to insert. They do not exist yet but will be inserted before the batch transaction completes. However, I cannot find information about how to set the Low values or how to get what Low value is up next. Any ideas?

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  • Low Profile AMD Cooling

    - by J. T.
    I have a few setups where I can mount two motherboards on top of each other. They are running AMD Athlon 64 x2 dual core 4200 CPU's using a very low profile CPU cooler. These coolers are loud and annoying. Does anyone know of a low profile QUIET CPU cooling solution?

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  • Notification of low DHCP pool in split scope setup

    - by JJBladester
    In Windows Server 2008 R2, it is possible to read the Event Viewer for EventID 1020 which is an indication that the DHCP pool is running low on addresses. What if I have two DHCP servers in my domain that use an 80/20 split scope to take a /24 pool of DHCP-allocated IP addresses and split it amongst the two servers according to this Technet Article? In this case, since the scope is split, how can I tell if the total DHCP pool, which is split amongst the two DHCP servers, is beginning to run low on address space?

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  • Low Profile AMD Cooling

    - by J. T.
    I have a few setups where I can mount two motherboards on top of each other. They are running AMD Athlon 64 x2 dual core 4200 CPU's using a very low profile CPU cooler. These coolers are loud and annoying. Does anyone know of a low profile QUIET CPU cooling solution?

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  • ssh during low bandwidth

    - by kfmfe04
    I currently invoke the following ssh command over my home wifi (from OSX to Ubuntu): ssh -XYC -l my_username -c arcfour,blowfish-cbc -XC my_local_server This works great, except during low bandwidth situations, like if I'm streaming music over the Web, while I'm coding. In these situations, the ssh often drops, within a minute or two. Is there a better setting or configuration that I can try over low-bandwidth situations?

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  • Of these 3 methods for reading linked lists from shared memory, why is the 3rd fastest?

    - by Joseph Garvin
    I have a 'server' program that updates many linked lists in shared memory in response to external events. I want client programs to notice an update on any of the lists as quickly as possible (lowest latency). The server marks a linked list's node's state_ as FILLED once its data is filled in and its next pointer has been set to a valid location. Until then, its state_ is NOT_FILLED_YET. I am using memory barriers to make sure that clients don't see the state_ as FILLED before the data within is actually ready (and it seems to work, I never see corrupt data). Also, state_ is volatile to be sure the compiler doesn't lift the client's checking of it out of loops. Keeping the server code exactly the same, I've come up with 3 different methods for the client to scan the linked lists for changes. The question is: Why is the 3rd method fastest? Method 1: Round robin over all the linked lists (called 'channels') continuously, looking to see if any nodes have changed to 'FILLED': void method_one() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } while(true) { for(std::size_t i = 0; i < channel_list.size(); ++i) { Data* current_item = channel_cursors[i]; ACQUIRE_MEMORY_BARRIER; if(current_item->state_ == NOT_FILLED_YET) { continue; } log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[i] = static_cast<Data*>(current_item->next_.get(segment)); } } } Method 1 gave very low latency when then number of channels was small. But when the number of channels grew (250K+) it became very slow because of looping over all the channels. So I tried... Method 2: Give each linked list an ID. Keep a separate 'update list' to the side. Every time one of the linked lists is updated, push its ID on to the update list. Now we just need to monitor the single update list, and check the IDs we get from it. void method_two() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } UpdateID* update_cursor = static_cast<UpdateID*>(update_channel.tail_.get(segment)); while(true) { if(update_cursor->state_ == NOT_FILLED_YET) { continue; } ::uint32_t update_id = update_cursor->list_id_; Data* current_item = channel_cursors[update_id]; if(current_item->state_ == NOT_FILLED_YET) { std::cerr << "This should never print." << std::endl; // it doesn't continue; } log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[update_id] = static_cast<Data*>(current_item->next_.get(segment)); update_cursor = static_cast<UpdateID*>(update_cursor->next_.get(segment)); } } Method 2 gave TERRIBLE latency. Whereas Method 1 might give under 10us latency, Method 2 would inexplicably often given 8ms latency! Using gettimeofday it appears that the change in update_cursor-state_ was very slow to propogate from the server's view to the client's (I'm on a multicore box, so I assume the delay is due to cache). So I tried a hybrid approach... Method 3: Keep the update list. But loop over all the channels continuously, and within each iteration check if the update list has updated. If it has, go with the number pushed onto it. If it hasn't, check the channel we've currently iterated to. void method_three() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } UpdateID* update_cursor = static_cast<UpdateID*>(update_channel.tail_.get(segment)); while(true) { for(std::size_t i = 0; i < channel_list.size(); ++i) { std::size_t idx = i; ACQUIRE_MEMORY_BARRIER; if(update_cursor->state_ != NOT_FILLED_YET) { //std::cerr << "Found via update" << std::endl; i--; idx = update_cursor->list_id_; update_cursor = static_cast<UpdateID*>(update_cursor->next_.get(segment)); } Data* current_item = channel_cursors[idx]; ACQUIRE_MEMORY_BARRIER; if(current_item->state_ == NOT_FILLED_YET) { continue; } found_an_update = true; log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[idx] = static_cast<Data*>(current_item->next_.get(segment)); } } } The latency of this method was as good as Method 1, but scaled to large numbers of channels. The problem is, I have no clue why. Just to throw a wrench in things: if I uncomment the 'found via update' part, it prints between EVERY LATENCY LOG MESSAGE. Which means things are only ever found on the update list! So I don't understand how this method can be faster than method 2. The full, compilable code (requires GCC and boost-1.41) that generates random strings as test data is at: http://pastebin.com/e3HuL0nr

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  • Which programming languages aren't considered high-level?

    - by hilo
    In informatics theory I hear and read about high-level and low-level languages all time. Yet I don't understand why this is still relevant as there aren't any (relevant) low-level languages except assembler in use today. So you get: Low-level Assembler Definitely not low-level C BASIC FORTRAN COBOL ... High-level C++ Ruby Python PHP ... And if assembler is low-level, how could you put for example C into the same list. I mean: C is extremely high-level compared to assembler. Same even for COBOL, Fortran, etc. So why does everybody keep mentioning high and low-level languages if assembler is really the only low-level language.

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  • Why does one loop take longer to detect a shared memory update than another loop?

    - by Joseph Garvin
    I've written a 'server' program that writes to shared memory, and a client program that reads from the memory. The server has different 'channels' that it can be writing to, which are just different linked lists that it's appending items too. The client is interested in some of the linked lists, and wants to read every node that's added to those lists as it comes in, with the minimum latency possible. I have 2 approaches for the client: For each linked list, the client keeps a 'bookmark' pointer to keep its place within the linked list. It round robins the linked lists, iterating through all of them over and over (it loops forever), moving each bookmark one node forward each time if it can. Whether it can is determined by the value of a 'next' member of the node. If it's non-null, then jumping to the next node is safe (the server switches it from null to non-null atomically). This approach works OK, but if there are a lot of lists to iterate over, and only a few of them are receiving updates, the latency gets bad. The server gives each list a unique ID. Each time the server appends an item to a list, it also appends the ID number of the list to a master 'update list'. The client only keeps one bookmark, a bookmark into the update list. It endlessly checks if the bookmark's next pointer is non-null ( while(node->next_ == NULL) {} ), if so moves ahead, reads the ID given, and then processes the new node on the linked list that has that ID. This, in theory, should handle large numbers of lists much better, because the client doesn't have to iterate over all of them each time. When I benchmarked the latency of both approaches (using gettimeofday), to my surprise #2 was terrible. The first approach, for a small number of linked lists, would often be under 20us of latency. The second approach would have small spats of low latencies but often be between 4,000-7,000us! Through inserting gettimeofday's here and there, I've determined that all of the added latency in approach #2 is spent in the loop repeatedly checking if the next pointer is non-null. This is puzzling to me; it's as if the change in one process is taking longer to 'publish' to the second process with the second approach. I assume there's some sort of cache interaction going on I don't understand. What's going on?

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  • Reducing latency for different geographic regions on Amazon Cloud

    - by Shoaibi
    I have got an application which has three components Application code : Amazon EC2 US-EAST-1 instance Application images, and other static data : Amazon S3 with CloudFront Application Database : Amazon RDS In short i need something like Cloud Front for EC2. In long, people using this application from a different region say middle east will have faster static content downloading due to Cloud Front but there would be a lot of latency in communicating to EC2 instance. I want to use a budget friendly way of enhancing this. Launching Amazon Instances in every region that offer is sure a choice, but isn't really cheap, so would try to avoid it unless its last resort. Also say if my clients also need to communicate to the RDS database directly, is there some kind of solution which gives that kind of functionality mentioned above, but for RDS?

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  • Local Live Quicktime Video Broadcast, latency?

    - by Snowwire
    I'm looking into the feasibility of using a local server to distribute live video of a conference to delegates in the same room. They would still hear the live audio coming from the speaker, so only the video would be streamed. I was considering a Darwin Steaming Server (a lot of iPhone users to support) and encoding with H.264. My main concern is latency across the network. Even with everything running locally, would there be lip sync issues between the live audio and the 'live' video stream? It feels like there will be problems given the encoding, broadcasting, decoding to be completed, but I've never done any like this before so thought I would check. Thanks

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  • HD latency measurement using bonnie++ on different machines with different RAM size

    - by j0nes
    Hello, I have run bonnie++ v1.96 on two different servers without any additional load. One server is a "physical" Dell server with 32GB RAM, the other one is a virtual instance with 14GB RAM. I have read in the bonnie manuals that I should use two times the size of RAM in my bonnie runs, so I used 64GB on the physical machine and 28GB on the virtual machine. Now I want to compare the results, and I am wondering whether the results are comparable at all. The most interesting part is the latency part - on the physical machine, the values are about 10 times higher than on the virtual machine! Can I take these results seriously (e.g. the virtual machine HD is much much faster) or does the different RAM size tamper the results? Thanks! Jonas

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  • Monitoring bandwidth/latency/jitter between 2 sites?

    - by TheCleaner
    I have 2 sites connected via an MPLS network and I'd like to do the following: setup a host on each end that can "talk" back and forth between each other and somehow report/log what kind of throughput, jitter, latency, etc. they are experiencing between each other in 5 minute intervals. Something similar to Qcheck but that can be automated. Bottom line is I'm trying to determine if the WAN network is "stable" throughout the day or if something is wrong. We have video conferences between these sites and even at 1024kbps calls we are experiencing delays and jitter. I'm hoping to exonerate the network with some testing.

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  • Tuning garbage collections for low latency

    - by elec
    I'm looking for arguments as to how best to size the young generation (with respect to the old generation) in an environment where low latency is critical. My own testing tends to show that latency is lowest when the young generation is fairly large (eg. -XX:NewRatio <3), however I cannot reconcile this with the intuition that the larger the young generation the more time it should take to garbage collect. The application runs on linux, jdk 6 before update 14, i.e G1 not available.

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  • High IO latency on ESXi 4.1 on HP DL580 G7

    - by teddydestodes
    at my Company we were experiencing some weird spikes on IO latency on one of our ESXi instances. we've spend 24h figuring out whats wrong and no clue so far. after giving up we put all the disks into a different server (HP DL380 G7) with much less RAM and only one 6(HT) cores (from 12 on the DL 580) which run fine for about 2 hours. I dont know the specs for the DL380 but both servers have a Smart Array P410i with BBWC (the DL 580 has 1GB) Is it possible that one(or all) of the disks is failing without actually failing?

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  • fast way to find network user computer on domain hogging all wan bandwidth

    - by dasko
    i have a network of about 40 domain users and i have huge latency wan issues, like 1400ms for google.com pings. I have noticed that the problem goes away after everyone goes home for the day. I would like to know if i should use something like a hub with wireshark on the router or modem to see if there are any irregular activity. I am open to suggestions but i need to isolate which user has the bug. I am assuming it is either downloads or someone spamming out heavily and not knowing. It would be best to trace to ip number so i can just look into dns and find the pc hostname with the problem? This is the first client i have this problem with so never really needed to address it before but not suprised as users don't actually listen to any best practices that we have suggested. Please help, thanks. just to update, pc's to routers and other computers have ping latency of 1ms so it is right after i hit the wan, using tracert to a web site (random), that i get the massive delay in the responses. As well this is a dsl line with 5mb down and 650kb up (maybe upload saturation?) thanks.

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  • Determining a realistic measure of requests per second for a web server

    - by Don
    I'm setting up a nginx stack and optimizing the configuration before going live. Running ab to stress test the machine, I was disappointed to see things topping out at 150 requests per second with a significant number of requests taking 1 second to return. Oddly, the machine itself wasn't even breathing hard. I finally thought to ping the box and saw ping times around 100-125 ms. (The machine, to my surprise, is across the country). So, it seems like network latency is dominating my testing. Running the same tests from a machine on the same network as the server (ping times < 1ms) and I see 5000 requests per second, which is more in-line with what I expected from the machine. But this got me thinking: How do I determine and report a "realistic" measure of requests per second for a web server? You always see claims about performance, but shouldn't network latency be taken into consideration? Sure I can serve 5000 request per second to a machine next to the server, but not to a machine across the country. If I have a lot of slow connections, they will eventually impact my server's performance, right? Or am I thinking about this all wrong? Forgive me if this is network engineering 101 stuff. I'm a developer by trade. Update: Edited for clarity.

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  • Determine asymmetric latencies in a network

    - by BeeOnRope
    Imagine you have many clustered servers, across many hosts, in a heterogeneous network environment, such that the connections between servers may have wildly varying latencies and bandwidth. You want to build a map of the connections between servers my transferring data between them. Of course, this map may become stale over time as the network topology changes - but lets ignore those complexities for now and assume the network is relatively static. Given the latencies between nodes in this host graph, calculating the bandwidth is a relative simply timing exercise. I'm having more difficulty with the latencies - however. To get round-trip time, it is a simple matter of timing a return-trip ping from the local host to a remote host - both timing events (start, stop) occur on the local host. What if I want one-way times under the assumption that the latency is not equal in both directions? Assuming that the clocks on the various hosts are not precisely synchronized (at least that their error is of the the same magnitude as the latencies involved) - how can I calculate the one-way latency? In a related question - is this asymmetric latency (where a link is quicker in direction than the other) common in practice? For what reasons/hardware configurations? Certainly I'm aware of asymmetric bandwidth scenarios, especially on last-mile consumer links such as DSL and Cable, but I'm not so sure about latency. Added: After considering the comment below, the second portion of the question is probably better off on serverfault.

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  • network latency, TCP and UDP packets

    - by user115848
    Hello recently my network has started to cause me lots of problems. I have a cable modem, connected to a tp-link router (with some port forwarding). Everything was working fine then i started to get lots of udp (port 53) "UNREPLIED" logs in the router. Now there are tcp UNREPLIED logs too. This is causing lots of latency and failed connections when trying to connect to different internet sites. Also, we run an openfire server for spark connections, and I believe its causing connectivity issues for some users who are trying to connect using Spark (some people connect fine, others don't). Please see screen shot below for packet logs. It has to be something internally, as I connected straight to the comcast modem and i was able to connect to the internet and various sites as normal. I tried to swap out the router with a different and got the same issue. I scanned both my internal dns servers for viruses or malware and it came up empty. Another anomaly is that when i try to connect to www.cnn.com, i get redirected to the different site. I scanned my own machine for hijacks. Not sure if this is related to the networking issue. Please let me know if you have any ideas for troubleshooting.

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  • Threads, Sockets, and Designing Low-Latency, High Concurrency Servers

    - by lazyconfabulator
    I've been thinking a lot lately about low-latency, high concurrency servers. Specifically, http servers. http servers (fast ones, anyway) can serve thousands of users simultaneously, with very little latency. So how do they do it? As near as I can tell, they all use events. Cherokee and Lighttpd use libevent. Nginx uses it's own event library performing much the same function of libevent, that is, picking a platform optimal strategy for polling events (like kqueue on *bsd, epoll on linux, /dev/poll on Solaris, etc). They all also seem to employ a strategy of multiprocess or multithread once the connection is made - using worker threads to handle the more cpu intensive tasks while another thread continues to listen and handle connections (via events). This is the extent of my understanding and ability to grok the thousand line sources of these applications. What I really want are finer details about how this all works. In examples of using events I've seen (and written) the events are handling both input and output. To this end, do the workers employ some sort of input/output queue to the event handling thread? Or are these worker threads handling their own input and output? I imagine a fixed amount of worker threads are spawned, and connections are lined up and served on demand, but how does the event thread feed these connections to the workers? I've read about FIFO queues and circular buffers, but I've yet to see any implementations to work from. Are there any? Do any use compare-and-swap instructions to avoid locking or is locking less detrimental to event polling than I think? Or have I misread the design entirely? Ultimately, I'd like to take enough away to improve some of my own event-driven network services. Bonus points to anyone providing solid implementation details (especially for stuff like low-latency queues) in C, as that's the language my network services are written in.

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  • Audio Streaming Latency

    - by killianmcc
    I'm writing a UDP local area network video chat system and have got the video and audio streams working. However I'm experiencing a little latency (about half a second) in the audio and was wondering what codecs would provide the least latency. I'm using NAudio (http://naudio.codeplex.com/) which provides me access to the following codecs for streaming; Speex Narrow Band (VBR) Speex Wide Band (16kHz)(VBR) Speex Ultra Wide Band (32kHz)(VBR) DSP Group TrueSpeech (8.5kbps) GSM 6.10 (13kbps) Microsoft ADPCM (32.8kbps) G.711 a-law (64kbps) G.722 16kHz (64kbps) G.711 mu-law (64kbps) PCM 8kHz 16 bit uncompressed (128kbps) I've tried them out and I'm not noticing much difference. Is there any others that I should download and try to reduce latency? I'm only going to be sending voice over the connection but I'm not really worried about quality or background noises too much. UPDATE I'm sending the audio in blocks like so; waveIn = new WaveIn(); waveIn.BufferMilliseconds = 50; waveIn.DeviceNumber = inputDeviceNumber; waveIn.WaveFormat = codec.RecordFormat; waveIn.DataAvailable += waveIn_DataAvailable; void waveIn_DataAvailable(object sender, WaveInEventArgs e) { if (connected) { byte[] encoded = codec.Encode(e.Buffer, 0, e.BytesRecorded); udpSender.Send(encoded, encoded.Length); } }

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  • javascript: is there any JS can test network speed?

    - by Bin Chen
    I am going to test my website speed, primary the webserver latency. Summarize what I want to achieve: 1) a webpage with javascript hosted in my website(http://myweb.com/test-speed.html) 2) I give this url to my friends 3) They don't need to do anything, they just need to access this webpage then the latency is printed out in the webpage. 4) If the webpage can also tell which state the visitor is in(using IP address range database), it will be a plus. Any existing solutions? I can modify the javascript to log the data into database, but I think the core here is how to writ the javascript to know the latency.

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  • Internet compression proxy for low speed broadband?

    - by user23150
    I live in a rural location, using high-latency wireless off a local ISP's tower. My speed tests vary day to day, but I can get around 1Mb up/down. The problem is, I work with large files, uploading and downloading (HD videos, development software, etc.). It can be painful to wait sometimes. Plus I do some side contract game development, and it can be very difficult to playtest with other developers (200ms ping is a good day for me). Now, obviously it's not going to be easy to solve the latency problem without different wireless hardware. But speedwise, I am wondering if I can use some kind of compression technology on a proxy. For instance, my work computer has full access to a 26Mb down, 10Mb up connection, that is totally unused at night and the weekends. If I could run some kind of compression technology on our server, and use it as a proxy to route to my home computer, I could stand to gain some major speed. I realize that by bogging down a system with compression, I could potentially lose whatever speed gain I had. But the proxy server is a quad core xeon, and the receiving computer is a pretty decent i7 computer, so that shouldn't be a concern. I found http://toonel.net/ but it seems more geared toward very slow narrowband users, like dial-up. Plus, I would prefer to just be able to point my browser to a proxy server, rather then install software on my client machine. EDIT I thought about my question a little more, and realize I am going to need to install software on my client in order to decompress, and possible compress (for uploading). That's not a huge deal.

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