Mag Gam put forth on 11/27/2010 11:06 AM: > Stan, > > Correct. On my severs I too have sound cards and USB. I don't really > need them so I would rather unload them. I suppose I can do a macro > benchmark and state if it helped or not but I would like to know on a > micro level to see if it helped. I think one possibility is to do > "lat_pipe" from lmbench to measure transaction latency of a UNIX pipe. > > My goal is to have the most optimal kernel/tuning since our > application is very latency sensitive.
In that case modules aren't your worry--the kernel interrupt timer is, along with scheduled tasks. For latency sensitive apps, you need a kernel with something like CONFIG_HZ=1000 or greater, which IIRC used to be the "workstation" default. The "server" default is 250Hz. Also, IIRC, the current Debian kernels implement tickless timers to allow better integration as virtual machine guests. For latency sensitive apps, you'd don't want a tickless timer. If you have a latency sensitive app: 1. Use a kernel with CONFIG_HZ=1000 (or greater) 2. Eliminate all possible cron jobs or schedule them to run at times when it won't impact the latency of your application. I.e. make sure no processes fire unexpectedly which may impact the latency of you application. On today's multicore systems this is less of a problem than it once was as your application can continue to run on the core which is executing it while a new process will be fired up on another core. When/if in doubt, minimize unexpected process execution. 3. If the application is disk I/O bound, make sure you have plenty of write cache, and a stripe (RAID6/10) of a sufficient number of spindles. RAID10 is optimal for low latency. RAID6 can suffer read-modify-write cycles which will increase latency. If you have large write cache, and your app never bursts an amount of data larger than the cache, then RAID6 may be fine. Testing is your friend here. Also note that the XFS filesystem offers the "realtime" sub volume which can decrease latency. It was originally developed for streaming media applications such as digital broadcast systems that replaced teh traditional tape systems: http://xfs.org/docs/xfsdocs-xml-dev/XFS_User_Guide//tmp/en-US/html/ch04s09.html 4. If the application is sensitive to network latency, use a NIC and driver that supports TCP offload processing. If the application needs DNS name resolution of remote systems, consider installing a local caching resolver such as pdns-recursor, which can reduce lookup latency considerably for cached results. -- Stan -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/4cf1df5b.6030...@hardwarefreak.com
