Re: [PATCH 4/5] select: make select() use schedule_hrtimeout()

Linus Torvalds
2008-08-29T16:20:58Z

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).

Linus