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KernelTrap: Running At 10,000 HZ

Dec 16, 2003, 03:00 (2 Talkback[s])

[ Thanks to Jeremy Andrews for this link. ]

"Jean-Marc Valin offered a patch on the lkml against the 2.6.0-test11 kernel adding the ability to increase the HZ all the way up to 10,000. In an earlier discussion about variable hertz, Robert Love talked about the impact of the 2.6 kernel increasing the default HZ from 100 up to 1000. Robert then explained, 'there are downsides, however. The major one is the increased timer overhead. Going from HZ=100 to HZ=1000 you have 10x more timer interrupts and thus 10x overhead. Now, on a fast system, timer overhead is probably negligible to begin with. Ten times nothing is still nothing. But on a slower system (by slow I mean 386 or 486 slow) it may be an issue.' On the plus side, Robert also then described how you can get better performance with a higher HZ.

"When asked why he needed a 10x increase to the already increased default 2.6 HZ setting, Jean-Marc humorously explained that he didn't like the CPU's ~1kHz idle sound, prefering instead to increase it to 10kHz, 'a frequency where the ear is much less sensitive.' This explanation lead to a quip from Nick Piggin, 'does it scare your dog away?', as well as a pointer from Tim Schmielau to other high-res-timer patches..."

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