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

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Message-ID: <alpine.LFD.2.03.1307191016010.14924@syhkavp.arg>
Date:	Fri, 19 Jul 2013 10:20:19 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Will Deacon <will.deacon@....com>
cc:	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>,
	Russell King <linux@....linux.org.uk>,
	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, 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.


Nicolas
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