linux-kernel - Re: [PATCH 2/2] Convert PowerPC macro spin_event_timeout() to architecture independent macro

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Date:	Wed, 31 Jul 2013 17:16:49 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Timur Tabi <timur@...i.org>
CC:	Arpit Goel <B44344@...escale.com>, linux@....linux.org.uk,
	takata@...ux-m32r.org, philb@....org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	linux390@...ibm.com, David Miller <davem@...emloft.net>,
	Rob Herring <rob.herring@...xeda.com>,
	Arnd Bergmann <arnd@...db.de>,
	Stephen Warren <swarren@...dia.com>, john.stultz@...aro.org,
	jesper.nilsson@...s.com, gregkh@...uxfoundation.org,
	sam@...nborg.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-m32r@...linux-m32r.org, linux-m32r-ja@...linux-m32r.org,
	linux-m68k@...r.kernel.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, mattw@...eaurora.org
Subject: Re: [PATCH 2/2] Convert PowerPC macro spin_event_timeout() to architecture
 independent macro

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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