linux-kernel - Re: [PATCH] locking/qrwlock: Allow multiple spinning readers

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Message-ID: <20160401103143.GJ3448@twins.programming.kicks-ass.net>
Date:	Fri, 1 Apr 2016 12:31:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@....com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] locking/qrwlock: Allow multiple spinning readers

On Thu, Mar 31, 2016 at 06:12:38PM -0400, Waiman Long wrote:
> >>However, if we allow a limited number of readers to spin on the
> >>lock simultaneously, we can eliminates some of the reader-to-reader
> >>latencies at the expense of a bit more cacheline contention and
> >>probably more power consumption.
> >So the embedded people might not like that much.
> 
> It could be. It is always a compromise.

So ARM is the only one that currently waits without spinning and could
care; so Will might have an opinion. One 'solution' would be to make
this an optional feature.