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SubjectRe: [rtl] Low-latency patches working GREAT (<2.9ms audio latency), see testresults ,but ISDN troubles
On Sun, Aug 29, 1999 at 09:15:19AM +0200, Ingo Molnar wrote:
> On Sat, 28 Aug 1999 wrote:
> > I'm concerned that the major improvement has come from additional
> > calls to schedule instead of from some basic improvements in algorithm.
> there are _no_ extra calls to schedule, only if necessery. Zero, nil,
> nada. Please check out the patch.

Tell me what I misunderstood. As far as I can tell, pre patch behavior
involves many fewer calls to schedule, post patch behavior for a write, for
example, can make at least one extra call to the scheduler for every block
copied. If "needs_resched >0" it is still not necessarily true that the
call to the scheduler is "necessary". Consider, a long running data base
program is writing backing store out to disk. Old behavior: the write
absorbs as much free memory as possible to optimize disk behavior. New
behavior: a screen saver, which is small i/o bound, causes needs resched
to be set continually, and the write is segmented into many smaller writes.
We now have, like NT, optimized the screen saver on a server while hammering
file system performance. Isn't that correct?

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