Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a configurable timer

Borislav Petkov
2015-05-20T20:16:03Z

On Wed, May 20, 2015 at 09:12:15PM +0200, Thomas Gleixner wrote:
> Which would be good enough for mdelay/udelay I think, but we'd need to
> measure the time spend in MWAITT so we wont return early.
>
> Something like this:

Yeah, with a check maybe:

> delay = usec_to_tsc(delay_usec);

if (delay > ((1 << 32) - 1)) {
mdelay(delay_usec);
return;
}

> end = rdtsc() + delay;
> while (1) {

I guess
monitorx( ...);

first.

> MWAITT(delay);
> now = rdtsc();
> if (end <= now)
> break;
> delay = end - now;
> }
>
> Now we'd need to add alternatives or some other mechanism to it to
> make this conditionally for those machines.

alternative_call(mdelay, mdelayx, X86_FEATURE_MWAITT, /* no output */, timeout);

Something like that maybe.

> Not sure if it's worth the trouble.

Could be a use case for MWAITX in the kernel!

:-D

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
--