Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756639AbZJFJB2 (ORCPT ); Tue, 6 Oct 2009 05:01:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754943AbZJFJB1 (ORCPT ); Tue, 6 Oct 2009 05:01:27 -0400 Received: from mail-yx0-f194.google.com ([209.85.210.194]:44624 "EHLO mail-yx0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754721AbZJFJB0 convert rfc822-to-8bit (ORCPT ); Tue, 6 Oct 2009 05:01:26 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=B5DQAbYL8HgnvT3hP3SFEs5zhBZ+mUBRjI6LfSeJ3FkHzTBvKq8zBqBAcFaLsqQkta PQCf5nZcFeRP4qGFsuYoA6J6JjYYohOxyX7i0M2OcenXzOFxUxowJyX2xi3CuZrq0/aa nquuCVlNc0IzbU2H1smpV57BfyJ0GN6Rxhkr0= MIME-Version: 1.0 In-Reply-To: <20091006084120.GJ5216@kernel.dk> References: <20091002195815.GE4494@redhat.com> <20091002222756.GG4494@redhat.com> <4e5e476b0910030543o776fb505ka0ce38da9d83b33c@mail.gmail.com> <20091003133810.GC12925@redhat.com> <4e5e476b0910040215m35af5c99pf2c3a463a5cb61dd@mail.gmail.com> <20091004121122.GB18778@redhat.com> <4e5e476b0910040546h5f77cd1fo3172fe5c229eb579@mail.gmail.com> <4e5e476b0910051409x33f8365flf32e8e7548d72e79@mail.gmail.com> <20091006084120.GJ5216@kernel.dk> Date: Tue, 6 Oct 2009 11:00:48 +0200 Message-ID: <4e5e476b0910060200i7c028b3fr4c235bf5f18c3aa1@mail.gmail.com> Subject: Re: Do we support ioprio on SSDs with NCQ (Was: Re: IO scheduler based IO controller V10) From: Corrado Zoccolo To: Jens Axboe Cc: Jeff Moyer , Vivek Goyal , Valdis.Kletnieks@vt.edu, Mike Galbraith , Ingo Molnar , Ulrich Lukas , linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, dm-devel@redhat.com, nauman@google.com, dpshah@google.com, lizf@cn.fujitsu.com, mikew@google.com, fchecconi@gmail.com, paolo.valente@unimore.it, ryov@valinux.co.jp, fernando@oss.ntt.co.jp, dhaval@linux.vnet.ibm.com, balbir@linux.vnet.ibm.com, righi.andrea@gmail.com, m-ikeda@ds.jp.nec.com, agk@redhat.com, akpm@linux-foundation.org, peterz@infradead.org, jmarchan@redhat.com, torvalds@linux-foundation.org, riel@redhat.com 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: 2410 Lines: 59 On Tue, Oct 6, 2009 at 10:41 AM, Jens Axboe wrote: > On Mon, Oct 05 2009, Corrado Zoccolo wrote: >> On Mon, Oct 5, 2009 at 5:06 PM, Jeff Moyer wrote: >> > It stands for residual, not residency.  Make more sense? >> It makes sense when computed, but not when used in rb_key computation. >> Why should we postpone queues that where preempted, instead of giving >> them a boost? > > We should not, if it is/was working correctly, it should allow both for > increase/descrease of tree position (hence it's a long and can go > negative) to account for both over and under time. I'm doing some tests with and without it. How it is working now is: definition: if (timed_out && !cfq_cfqq_slice_new(cfqq)) { cfqq->slice_resid = cfqq->slice_end - jiffies; cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid); } * here resid is > 0 if there was residual time, and < 0 if the queue overrun its slice. use: rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies; rb_key += cfqq->slice_resid; cfqq->slice_resid = 0; * here if residual is > 0, we postpone, i.e. penalize. If residual is < 0 (i.e. the queue overrun), we anticipate it, i.e. we boost it. So this is likely not what we want. I did some tests with and without it, or changing the sign, and it doesn't matter at all for pure sync workloads. The only case in which it matters a little, from my experiments, is for sync vs async workload. Here, since async queues are preempted, the current form of the code penalizes them, so they get larger delays, and we get more bandwidth for sync. This is, btw, the only positive outcome (I can think of) from the current form of the code, and I think we could obtain it more easily by unconditionally adding a delay for async queues: rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies; if (!cfq_cfqq_sync(cfqq)) { rb_key += CFQ_ASYNC_DELAY; } removing completely the resid stuff (or at least leaving us with the ability of using it with the proper sign). Corrado > > -- > Jens Axboe > > -- 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/