|| ||Linus Torvalds <torvalds-AT-linux-foundation.org>|
|| ||Arjan van de Ven <arjan-AT-infradead.org>|
|| ||Re: [PATCH 4/5] select: make select() use schedule_hrtimeout()|
|| ||Fri, 29 Aug 2008 09:20:18 -0700 (PDT)|
|| ||linux-kernel-AT-vger.kernel.org, mingo-AT-elte.hu, tglx-AT-tglx.de|
On Fri, 29 Aug 2008, Arjan van de Ven wrote:
> now that we have schedule_hrtimeout(), make select() use it.
> But only for short delays; really long delays are assumed to not
> need the highres level of accuracy but rather want the regular
> timer behavior for now.
This is _really_ ugly.
Can't you just do this relaxation in "schedule_hrtimeout()" instead, and
just document the fact that the "high resolution" of hrtimeout is relative
to the length of the timeout.
It's not that select() doesn't care, it's that *NOBODY* cares. If somebody
asks for a timeout of one second and 2 microseconds, the two microseconds
simply don't matter. Ever. But if somebody asks for a timeout of 12
microseconds, individual microseconds probably _do_ matter.
So if you want high-resolution select/poll, then get rid of the "use_hr"
logic entirely, and just do it unconditionally. Then, relax the scheduler
timeouts in the scheduler.
(But, that's probably _generally_ true. Even now, when people do
"schedule_timeout()", there's a big difference between asking for two
ticks and asking for two seconds. The latter should probably try to round
to a nice timer tick basis for power reasons).
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