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SubjectRe: Overscheduling DOES happen with high web server load.
On Fri, May 07, 1999 at 03:34:56AM -0700, Jim Gettys wrote:
> 100hz == 10 ms == about 1/3 - 1/6 of human perception or your latency
> budget for actions to be percieved as truly "instantaneous"; you
> never can get latency back.
> Given Jay's recent mail on the topic, I think things jibe with my memory:
> the console is set that high in large part since we run that fast on other
> operating systems; this got set as part of the initial experiments when
> porting to new architectures; the cost of running at a high basic
> rate is low enough that this was a rational design decision.
> - Jim

1) Please note that the overscheduling problem was NOT caused by HZ being
high. (I guess you know, I just wanted to point out again.)
2) The kernel can wake up processes immediately, if they blocked on I/O
before, orif they get a signal, so the interactive feeling does not
necessarily on HZ. From what I know, the Linux kernel does it that way.
3) There might still be cases where processes should be scheduled ASAP but
are only on the next scheduler tick. I got some multithreaded (pthreads)
numerical benchmark which depends on the HZ setting. (At least it did,
when I last tested (2.2.2 or smth similar), but maybe Ingo has changed
something soince then.)
This is the reason for my HZ=400 on ix86 patch.

Kurt Garloff <> SuSE GmbH, Nürnberg, FRG
Linux kernel development; SCSI driver: DC390 (tmscsim/AM53C974)
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