From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 609326B0012 for ; Tue, 31 May 2011 00:36:50 -0400 (EDT) Received: from m3.gw.fujitsu.co.jp (unknown [10.0.50.73]) by fgwmail6.fujitsu.co.jp (Postfix) with ESMTP id 552C03EE0AE for ; Tue, 31 May 2011 13:36:46 +0900 (JST) Received: from smail (m3 [127.0.0.1]) by outgoing.m3.gw.fujitsu.co.jp (Postfix) with ESMTP id 3A33B45DE9C for ; Tue, 31 May 2011 13:36:46 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (s3.gw.fujitsu.co.jp [10.0.50.93]) by m3.gw.fujitsu.co.jp (Postfix) with ESMTP id 1B50745DE98 for ; Tue, 31 May 2011 13:36:46 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 0F63FE08001 for ; Tue, 31 May 2011 13:36:46 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.240.81.134]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id CF4DA1DB8037 for ; Tue, 31 May 2011 13:36:45 +0900 (JST) Date: Tue, 31 May 2011 13:29:50 +0900 From: KAMEZAWA Hiroyuki 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Rakib Mullick Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Christoph Lameter , Mel Gorman , KOSAKI Motohiro 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: > >> A A A A "Adding a cond_resched() to allow other threads to run in the > >> non-preemptive > >> A A 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, 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