Re: [PATCH 2/2] Convert PowerPC macro spin_event_timeout() to architectureindependent macro

From: Stephen Boyd
Date: Wed Jul 31 2013 - 20:16:59 EST

On 07/31/13 17:13, Timur Tabi wrote:
> On 07/31/2013 07:04 PM, Stephen Boyd wrote:
>> If it yields why are we using udelay? Why not usleep_range()? It would
>> be useful to have a variant that worked in interrupt context and it
>> looked like that was almost possible.
> I've never heard of usleep_range() before, so I don't know if it
> applies. Apparently, udelay() includes its own call to cpu_relax(). Is
> it possible that cpu_relax() is a "lightweight" yield, compared to sleeping?

cpu_relax() is usually just a compiler barrier or an instruction hint to
the cpu that it should cool down because we're spinning in a tight loop.
It certainly shouldn't be calling into the scheduler.

> FYI, you might want to look at the code reviews for spin_event_timeout()
> on the linuxppc-dev mailing list, back in March 2009.

Sure. Any pointers? Otherwise I'll go digging around the archives.

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