Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965647Ab0GPNw2 (ORCPT ); Fri, 16 Jul 2010 09:52:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54980 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965477Ab0GPNw1 (ORCPT ); Fri, 16 Jul 2010 09:52:27 -0400 Date: Fri, 16 Jul 2010 09:52:11 -0400 From: Vivek Goyal To: Gui Jianfeng Cc: Jens Axboe , Jeff Moyer , Corrado Zoccolo , linux kernel mailing list Subject: Re: [PATCH] CFQ: delay getting cfq group at the very point we really need it Message-ID: <20100716135211.GB15382@redhat.com> References: <4C3E6B78.6070808@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C3E6B78.6070808@cn.fujitsu.com> User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1723 Lines: 51 On Thu, Jul 15, 2010 at 09:59:20AM +0800, Gui Jianfeng wrote: > Delay searching or allocating a cfq group at the very point that > we really need it. This change would save some cycles every time > we're getting a cfq queue. > > Signed-off-by: Gui Jianfeng > --- > block/cfq-iosched.c | 5 +++-- > 1 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index eb4086f..9b0cf13 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -2820,10 +2820,8 @@ cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync, > { > struct cfq_queue *cfqq, *new_cfqq = NULL; > struct cfq_io_context *cic; > - struct cfq_group *cfqg; > > retry: > - cfqg = cfq_get_cfqg(cfqd, 1); > cic = cfq_cic_lookup(cfqd, ioc); > /* cic always exists here */ > cfqq = cic_to_cfqq(cic, is_sync); > @@ -2852,6 +2850,9 @@ retry: > } > > if (cfqq) { > + struct cfq_group *cfqg; > + > + cfqg = cfq_get_cfqg(cfqd, 1); > cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync); Gui, I noticed that once we have setup a cfqq and cfqg, for subequent requests we should not come into this function at all because in cfq_set_request(), cic will have pointer to cfqq. So I am not sure in what call path there is substantial saving but anyway, it should not harm moving cfq_get_cfqg() call down and call it after cfqq has been allocated. Acked-by: Vivek Goyal Thanks Vivek -- 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/