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SubjectRe: [patch] lowlatency patch for 2.4, lowlatency-2.4.0-test6-B5
yodaiken@fsmlabs.com wrote:
>
> On Fri, Aug 04, 2000 at 03:43:15PM +0200, Ingo Molnar wrote:
> > *no*. There are places in the kernel that do work for millisecs while
> > holding a spinlock. This causes millisec latencies even if we had a
>
> The interesting question here is "why"? The only example ever discussed
> here was copying data on big reads/writes and this seems like a classic
> case of where the algorithm needs to be fixed -- if you have a millisecond
> copy then you almost certainly would benefit from kiobufs or something smart.

The only expensive one which of which I'm aware is the lock in
zap_page_range(): "This is a long-lived spinlock.".

My approach here was to bust zap_page_range() up into 512-page chunks with
one reschedule per chunk. Ingo's patch does this on a per-page basis: tests
need_resched and then, if required, drops the lock and reschedules.

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