linux-kernel - Re: [PATCH v4 02/17] sched_clock: Use seqcount instead of rolling our own

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Message-ID: <20130719142718.GG24642@n2100.arm.linux.org.uk>
Date:	Fri, 19 Jul 2013 15:27:18 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	Will Deacon <will.deacon@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	John Stultz <john.stultz@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Christopher Covington <cov@...eaurora.org>
Subject: Re: [PATCH v4 02/17] sched_clock: Use seqcount instead of rolling
	our own

On Fri, Jul 19, 2013 at 10:20:19AM -0400, Nicolas Pitre wrote:
> On Fri, 19 Jul 2013, Will Deacon wrote:
> 
> > Looks good to me. The current scheme would be very fiddly to extend to
> > 64-bit values on 32-bit architectures without cheap atomic doubleword
> > accesses.
> 
> You should have a look at include/linux/cnt32_to_63.h.
> This could be applied to pure software counters if the low part is 
> atomically increased.

But this can't be used for sched_clock().  That's exactly why I originally
had to rewrite that thing in the first place.
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