From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta12.messagelabs.com (mail6.bemta12.messagelabs.com [216.82.250.247]) by kanga.kvack.org (Postfix) with ESMTP id BC4F66B0012 for ; Mon, 30 May 2011 23:58:41 -0400 (EDT) Received: by yib18 with SMTP id 18so2040695yib.14 for ; Mon, 30 May 2011 20:58:40 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110531121815.67523361.kamezawa.hiroyu@jp.fujitsu.com> References: <1306774744.4061.5.camel@localhost.localdomain> <20110531083859.98e4ff43.kamezawa.hiroyu@jp.fujitsu.com> <20110531121815.67523361.kamezawa.hiroyu@jp.fujitsu.com> Date: Tue, 31 May 2011 09:58:40 +0600 Message-ID: Subject: Re: [PATCH] mm, vmstat: Use cond_resched only when !CONFIG_PREEMPT From: Rakib Mullick Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Christoph Lameter , Mel Gorman , KOSAKI Motohiro 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_stat= s()) added cond_resched() in refresh_cpu_vm_stats. Purpose of that patch wa= s to allow other threads to run in non-preemptive case. This patch, makes s= ure that cond_resched() gets called when !CONFIG_PREEMPT is set. In a preem= ptiable 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 di= rectly ? >> > 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: >> =A0 =A0 =A0 =A0 "Adding a cond_resched() to allow other threads to run i= n the >> non-preemptive >> =A0 =A0 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_PREEM= PT ? > 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, Rakib > Thanks, > -Kame > > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org