From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751663Ab3KRWaV (ORCPT ); Mon, 18 Nov 2013 17:30:21 -0500 Received: from www.sr71.net ([198.145.64.142]:36889 "EHLO blackbird.sr71.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751281Ab3KRWaT (ORCPT ); Mon, 18 Nov 2013 17:30:19 -0500 Message-ID: <528A94C4.80101@sr71.net> Date: Mon, 18 Nov 2013 14:29:24 -0800 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Naoya Horiguchi CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org, dave.jiang@intel.com, akpm@linux-foundation.org, dhillf@gmail.com, Mel Gorman Subject: Re: [PATCH] mm: call cond_resched() per MAX_ORDER_NR_PAGES pages copy References: <20131115225550.737E5C33@viggo.jf.intel.com> <20131115225553.B0E9DFFB@viggo.jf.intel.com> <1384800714-y653r3ch-mutt-n-horiguchi@ah.jp.nec.com> <1384800841-314l1f3e-mutt-n-horiguchi@ah.jp.nec.com> <528A6448.3080907@sr71.net> <1384806022-4718p9lh-mutt-n-horiguchi@ah.jp.nec.com> <528A7D36.5020500@sr71.net> <1384811778-7euptzgp-mutt-n-horiguchi@ah.jp.nec.com> In-Reply-To: <1384811778-7euptzgp-mutt-n-horiguchi@ah.jp.nec.com> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/18/2013 01:56 PM, Naoya Horiguchi wrote: >> > Why bother trying to "optimize" it? > I thought that if we call cond_resched() too often, the copying thread can > take too long in a heavy load system, because the copying thread always > yields the CPU in every loop. I think you're confusing cond_resched() and yield(). The way I look at it: yield() means: "Hey scheduler, go right now and run something else I'm done running" cond_resched() means: "Schedule me off if the scheduler has already decided something else _should_ be running" I'm sure I'm missing some of the subtleties, but as I see it, yield() actively goes off and finds something else to run. cond_resched() only schedules you off if you've *already* run too long.