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Message-ID: <20130821164146.GA15194@redhat.com>
Date: Wed, 21 Aug 2013 18:41:46 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>,
Fernando Luis Vázquez Cao
<fernando_b1@....ntt.co.jp>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock
On 08/21, Peter Zijlstra wrote:
>
> The other consideration is that this adds two branches to the normal
> schedule path. I really don't know what the regular ratio between
> schedule() and io_schedule() is -- and I suspect it can very much depend
> on workload -- but it might be a net loss due to that, even if it makes
> io_schedule() 'lots' cheaper.
Yes, agreed. Please ignore it for now, I didn't try to actually suggest
this change. And even if this is fine perfomance wise, this needs some
benchmarking.
Well. actually I have a vague feeling that _perhaps_ this change can
help to solve other problems we are discussing, but I am not sure and
right now I can't even explain the idea to me.
In short: please ignore ;)
Oleg.
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