linux-kernel - Re: [PATCH 6/6] ARCv2: spinlock/rwlock: Reset retry delay when starting a new spin-wait cycle

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Message-ID: <20150803114352.GL25159@twins.programming.kicks-ass.net>
Date:	Mon, 3 Aug 2015 13:43:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, arc-linux-dev@...opsys.com
Subject: Re: [PATCH 6/6] ARCv2: spinlock/rwlock: Reset retry delay when
 starting a new spin-wait cycle

On Mon, Aug 03, 2015 at 03:33:08PM +0530, Vineet Gupta wrote:
> A spin lock could be available momentarily, but the SCOND to actually
> acquire it might still fail due to concurrent update from other core(s).
> To elide hardware lock, the sequence is retried after a "delay" which is
> increased expoenntially to get a nice backoff behaviour.
> 
> However, this could cause the delay counter to get to a high value. Thus
> when the next spin cycle restarts, reset the counter back to starting
> value of 1.


Cute.. fwiw, did you look at what Sparc64 does?
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