Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755838Ab1EaEgs (ORCPT ); Tue, 31 May 2011 00:36:48 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:53748 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750850Ab1EaEgr (ORCPT ); Tue, 31 May 2011 00:36:47 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Tue, 31 May 2011 13:29:50 +0900 From: KAMEZAWA Hiroyuki To: Rakib Mullick Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Christoph Lameter , Mel Gorman , KOSAKI Motohiro Subject: Re: [PATCH] mm, vmstat: Use cond_resched only when !CONFIG_PREEMPT Message-Id: <20110531132950.258cd16d.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <1306774744.4061.5.camel@localhost.localdomain> <20110531083859.98e4ff43.kamezawa.hiroyu@jp.fujitsu.com> <20110531121815.67523361.kamezawa.hiroyu@jp.fujitsu.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.1.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2327 Lines: 62 On Tue, 31 May 2011 09:58:40 +0600 Rakib Mullick wrote: > On Tue, May 31, 2011 at 9:18 AM, KAMEZAWA Hiroyuki > wrote: > > On Tue, 31 May 2011 09:13:47 +0600 > > Rakib Mullick wrote: > > > >> On Tue, May 31, 2011 at 5:38 AM, KAMEZAWA Hiroyuki > >> wrote: > >> > On Mon, 30 May 2011 22:59:04 +0600 > >> > Rakib Mullick wrote: > >> > > >> >> commit 468fd62ed9 (vmstats: add cond_resched() to refresh_cpu_vm_stats()) added cond_resched() in refresh_cpu_vm_stats. Purpose of that patch was to allow other threads to run in non-preemptive case. This patch, makes sure that cond_resched() gets called when !CONFIG_PREEMPT is set. In a preemptiable kernel we don't need to call cond_resched(). > >> >> > >> >> Signed-off-by: Rakib Mullick > >> > > >> > Hmm, what benefit do we get by adding this extra #ifdef in the code directly ? > >> > Other cond_resched() callers are not guilty in !CONFIG_PREEMPT ? > >> > > >> Well, in preemptible kernel this context will get preempted if > >> requires, so we don't need cond_resched(). If you checkout the git log > >> of the mentioned commit, you'll find the explanation. It says: > >>         "Adding a cond_resched() to allow other threads to run in the > >> non-preemptive > >>     case." > >> > > > > IOW, my question is "why only this cond_resched() should be fixed ?" > > cond_resched() forces this thread to be scheduled. I'm just trying > pointing out the use of cond_resched(), until unless I'm not missing > anything. > > > What's bad with all cond_resched() in the kernel as no-op in CONFIG_PREEMPT ? > > > cond_resched() basically checks whether it needs to be scheduled or > not. But, we know in advance that we don't need cond_resched in > CONFIG_PREEMPT. > > Thanks, Then just remove _all_ cond_resched() by defining noop function in header. Please don't fix in ugly way. #ifdef CONFIG_PEERMPT static void cond_resched() { } #endif Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/