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

[Huang Rui]

On Thu, May 21, 2015 at 04:15:54AM +0800, Borislav Petkov wrote:
> 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!
> 

Looks like good use case. Boris, could we try to implement it?

Thanks,
Rui
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/