On Fri, 16 Nov 2007 08:17:08 +0100 Ingo Molnar <[EMAIL PROTECTED]> wrote:
>
> * Andrew Morton <[EMAIL PROTECTED]> wrote:
>
> > It sounds like it would work OK. What is the setup cost for a usleep?
> > I'd have thought that code which does something like
> >
> > while (i++ < 1000) {
> > foo();
> > udelay(1);
> > }
> >
> > would take qiute a bit longer with such a change?
>
> full roundtrip cost ought to be below 10 usecs, depending on the system.
Ow. So the above timeout would take 10x longer. That probably won't break
anything, but quite a few drivers do udelay(1) for post-IO settling times
and they might not like it.
> There's no problem doing a non-preemptible udelay up to 10 usecs and we
> could use usleep above that.
Yup, with a few smarts in there we could work out which is the best to use,
and also compensate for the setup costs.
It doesn't sound very 2.6.24ish though.
As a quicky things perhaps we could only do the
preempt_disable()/preempt_enable()
if the TSCs are unsynced? Do we reliably know that? I guess not..
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
