Re: [RFC PATCH] Turn off the tick even when not idle

From: Pavel Machek
Date: Wed Sep 02 2009 - 16:01:45 EST


> When a process does some number crunching for a while, without involving
> the kernel, the kernel still interrupts it HZ times per second to figure
> out if it has any work to do. With a system dedicated to doing such
> number crunching, the answer will almost always come up "no"; however,
> the kernel takes a while figuring out all the "no"s from various
> subsystems, every timer tick. On my system, the timer tick takes about
> 80us, every 1/HZ seconds; that represents a significant overhead. 80us
> out of every 1ms, for instance, means 8% overhead. Furthermore, the
> time taken varies, and the timer interrupts lead to jitter in the
> performance of the number crunching.

8% overhead on hz=1000 is quite high --- what hw is that?

You should be able to get similar results with HZ=1, right?

(cesky, pictures)
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