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Kernel Timer Frequency
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Posted by PCS-Chris, 11-28-2009, 04:54 PM Just wondering what peoples opinions are on Timer Frequencies on systems with different setups? I've never really looked into this much before. Obviously on the desktop/multimedia and gameservers a 1000Hz Kernel is preferable. But is 1000Hz really needed on a webhosting machine, i.e. if you take a typical cPanel server as an example. I might have been looking at Xen for too long but I thought the CentOS5 kernel was 250Hz by default. It looks like it's 1000Hz now on the latest version. What do you run and any certain reason why? Chris
Posted by soulhunter, 11-28-2009, 07:56 PM Hi! I find that kernel tick frequency is only useful when it comes to multimedia, or maybe control systems (industrial), as for typical web APPs: no, you don't actually need to care about it that much. I even think that, in recent kernels, it is more often used "tickless kernel", so, you could, in theory (and If I understood correctly), have 1000Hz tick frequency, and still don't be wasting CPU on context switching, just increase the timer resolution... but, once again, I'm not sure how the tickless kernel is related to the tick frequency. When there was no tickless kernel, a lower kernel frequency (even down to 100Hz) could increase the *raw* processing power available for a small number of tasks (calculation cluster, for example), but then you was unable to run more than 100 tasks/second, and the timer resolution went down, and, the more ticks per second, more overhead went to context switching, and you reduced the raw processing power, so, back in these times, there was a trade-off. Now, there is also the kernel preemption, but that's another history (although related). I hope this helps, Ildefonso Camargo
Posted by ramnet, 11-29-2009, 10:00 PM I like to run the timer at 100 Mhz - it was the standard linux timer frequency for many years and that's good enough for me. Plus, at 100 Mhz Netcraft will generate a nice uptime graph for you
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