linux-kernel - Re: [PATCH] CPU hotplug, writeback: Don't call writeback_set

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Message-ID: <20120928122719.GA3067@localhost>
Date:	Fri, 28 Sep 2012 20:27:19 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Borislav Petkov <bp@...64.org>,
	Conny Seidel <conny.seidel@....com>, Jan Kara <jack@...e.cz>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] CPU hotplug, writeback: Don't call
 writeback_set_ratelimit() too often during hotplug

On Tue, Sep 25, 2012 at 02:18:20AM +0530, Srivatsa S. Bhat wrote:
> 
> From: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> 
> The CPU hotplug callback related to writeback calls writeback_set_ratelimit()
> during every state change in the hotplug sequence. This is unnecessary
> since num_online_cpus() changes only once during the entire hotplug operation.
> 
> So invoke the function only once per hotplug, thereby avoiding the
> unnecessary repetition of those costly calculations.
> 
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> ---

Looks good to me. I'll include it in the writeback tree.

Thanks,
Fengguang
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