Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756879Ab1CaD76 (ORCPT ); Wed, 30 Mar 2011 23:59:58 -0400 Received: from smtp-out.google.com ([216.239.44.51]:1818 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753515Ab1CaD75 convert rfc822-to-8bit (ORCPT ); Wed, 30 Mar 2011 23:59:57 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=E+ZRlmj5zNoiYbKCC0r82GMv1k/inecog2U+LDXNbNab3R6UjcRynF9ZruzgQ1d64y yUrCW5d1niswEedYHJ5A== MIME-Version: 1.0 In-Reply-To: <20110330183446.GG1291@redhat.com> References: <4D8C48B6.6050300@fusionio.com> <20110330183446.GG1291@redhat.com> From: Justin TerAvest Date: Wed, 30 Mar 2011 20:59:34 -0700 Message-ID: Subject: Re: Why do we use cpu nice priority for ioprio? To: Vivek Goyal Cc: Jens Axboe , lkml , Chad Talbott Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1998 Lines: 51 On Wed, Mar 30, 2011 at 11:34 AM, Vivek Goyal wrote: > On Wed, Mar 30, 2011 at 11:23:45AM -0700, Justin TerAvest wrote: >> On Fri, Mar 25, 2011 at 12:48 AM, Jens Axboe wrote: >> > On 2011-03-25 03:38, Justin TerAvest wrote: >> >> It's not clear why the cpu nice value should be mapped to the ioprio >> >> for a task when none is picked. >> >> >> >> Internally, at cfq_init_prio_data(), we just set: >> >> ? ? ? ? ? ? ? ioprio = IOPRIO_NORM; >> >> ? ? ? ? ? ? ? ioprio_class = IOPRIO_CLASS_BE; >> >> if ioprio_class is IOPRIO_CLASS_NONE. >> >> >> >> >> >> The problem is that ?today, SCHED_RR and SCHED_FIFO threads >> >> automatically get bumped up to RT class. This all happens behind the >> >> curtains and the io_class of the thread is still shown as NONE with >> >> sys_ioprio_get(). What's the motivation behind this promotion of >> >> ioprio class? >> > >> > It was decided back in the day when io priorities were introduced. I >> > still think it's a good idea. >> >> This is the part I'm especially curious about. If we're managing the >> resources separately, >> why should be be adjusting io_class based on the nice value? > > What's wrong with taking a hint about ioclass and ioprio from cpu > scheduling class and nice value? I guess it's fine. I was just curious how strongly everyone felt about the way it works today. It sounds like we expect nice values and io scheduling classes to be closely matched. Thanks, Justin > > I think in general if some task is important from cpu perspective then > most likely it is important from IO perspective too. And if user thinks > otherwise, then one can explicitly set ioclass and ioprio of the task. > > So this makes sense to me. > > 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/