From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758112Ab0FUXF1 (ORCPT ); Mon, 21 Jun 2010 19:05:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41058 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754364Ab0FUXF0 (ORCPT ); Mon, 21 Jun 2010 19:05:26 -0400 Date: Mon, 21 Jun 2010 19:05:18 -0400 From: Vivek Goyal To: Moyer Jeff Moyer Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] cfq: always return false from should_idle if slice_idle is set to zero Message-ID: <20100621230518.GA10105@redhat.com> References: <1277149789-4493-1-git-send-email-jmoyer@redhat.com> <1277149789-4493-2-git-send-email-jmoyer@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1277149789-4493-2-git-send-email-jmoyer@redhat.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 On Mon, Jun 21, 2010 at 03:49:48PM -0400, Jeff Moyer wrote: > Hi, > > In testing a competing fsync-ing process and a sequential reader on > mid-grade storage, I found that cfq was incapable of achieving the I/O > rates of deadline, no matter how it was tuned. Investigation, and insight > from Vivek (mostly the latter), led to identifying that we were still > idling for the last queue in the service tree. > > Modifying cfq_should_idle to not idle when slice_idle is set to zero got > us much closer to the performance of deadline for this workload. I have > one follow-on patch that gets us on-par with deadline, but I think this > patch stands alone. > > Comments, as always, are appreciated. > Looks good to me Jeff. This does take away one functionality and that is ability to get group service differentation even with slice_idle=0. cfq_should_idle() was making sure that we don't select the next queue from next group. But I think a better way to fix that would be to introduce a new tunable say group_idle. That way if we are running on some powerful storage box and don't want the overhead of idling, we can do slice_idle=0 and not idle among the cfqq's with-in group but still do idle a bit on group and get the group service differentiation. I have a small patch for implementing group_idle. I will post that once you patch is in Jens's tree. Thanks Vivek > Cheers, > Jeff > > Signed-off-by: Jeff Moyer > --- > block/cfq-iosched.c | 4 ++++ > 1 files changed, 4 insertions(+), 0 deletions(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index 5ff4f48..572a050 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -1842,6 +1842,10 @@ static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq) > if (prio == IDLE_WORKLOAD) > return false; > > + /* Don't idle if slice idling is disabled by the user */ > + if (cfqd->cfq_slice_idle == 0) > + return false; > + > /* We do for queues that were marked with idle window flag. */ > if (cfq_cfqq_idle_window(cfqq) && > !(blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag)) > -- > 1.6.5.2 > > -- > 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/