Re: Why HZ on i386 is 100 ?

David Mosberger
2002-04-22T17:25:00Z

>>>>> On Sun, 21 Apr 2002 18:00:22 +0000, Pavel Machek <pavel@suse.cz> said:

Pavel> .5% still looks like a lot to me. Good compiler optimization
Pavel> is .5% on average...

Umh, but those optimizations are interesting only if they're
cumulative, i.e., once you've got 10 of them and they make a *total*
difference of 5% (actually, I'm doubtful anyone really notices
differences of 20-30% other than for benchmarking purposes... ;-).

For me, 1% is the magic threshold. If we find real apps that get a
higher penalty than that, I'd either lower the HZ or see if we can
tune the timer tick to be within a safe margin.

No matter what, though, higher tick rate clearly incurs somewhat
higher overhead. The benefit is lower application-level response time
and finer-granularity timeouts. I assume Robert has all the
benchmarks to show that. ;-)

--david