From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752056Ab1K1PTR (ORCPT ); Mon, 28 Nov 2011 10:19:17 -0500 Received: from postman.teamix.net ([194.150.191.120]:32971 "EHLO rproxy.teamix.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750795Ab1K1PTQ convert rfc822-to-8bit (ORCPT ); Mon, 28 Nov 2011 10:19:16 -0500 From: Martin Steigerwald Organization: teamix GmbH To: Jens Axboe Subject: [PATCH 1/1] Mention that I/O priorities also work on direct writes. Date: Mon, 28 Nov 2011 16:19:12 +0100 User-Agent: KMail/1.13.7 (Linux/3.1.0-1-686-pae; KDE/4.6.5; i686; ; ) Cc: linux-kernel@vger.kernel.org, Vivek Goyal References: <201111281542.22258.ms@teamix.de> <4ED39EA5.4000706@kernel.dk> In-Reply-To: <4ED39EA5.4000706@kernel.dk> MIME-Version: 1.0 Content-Type: Text/Plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Message-Id: <201111281619.12924.ms@teamix.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am Montag, 28. November 2011 schrieb Jens Axboe: > On 2011-11-28 15:42, Martin Steigerwald wrote: > > Hi jens und Vivek, > > > > Vivek, I cc'd you, cause you wrote the new cfq-iosched.txt. > > > > > > In trying to understand how I/O priorities actually really work, I tried > > to dd with > > > > rm nullen-id ; sync ; /usr/bin/time ionice -c3 dd if=/dev/zero > > of=nullen-id count=500 bs=1M conv=fsync > > > > versus > > > > rm nullen-rl; sync ; /usr/bin/time ionice -c1 -n0 dd if=/dev/zero > > of=nullen-rl count=500 bs=1M conv=fsync > > > > concurrently. No differences. At first I was puzzled, then I thought > > maybe direct I/O makes a difference. So I tried with oflag=direct. > > > > And it does. > > > > Then I actually read the documentation block/ioprio.txt (3.1 here): > >> With the introduction of cfq v3 (aka cfq-ts or time sliced cfq), basic > >> io priorities are supported for reads on files. This enables users to > >> io nice processes or process groups, similar to what has been possible > >> with cpu scheduling for ages. This document mainly details the current > >> possibilities with cfq; other io schedulers do not support io priorities > >> thus far. > > > > According to it I/O priorities will even only work on reads. Is that > > correct? I mean they do work on reads, I tested it, but *only* on reads? > > > > From what I see here, it also works for direct I/O write requests > > > > So from what I conclude is that CFQ I/O priorities work for all requests > > that are issued via synchronous system calls, but not for those issued > > via asynchronous calls, i. e. everything that goes through the > > pagecache. > > > > Is that correct? > > Priorities work for reads AND direct writes. In other words, it does not > work for buffered writes. > > > Vivek, one thing on cfq-iosched.txt: Could slice_idle=0 make sense on > > SSDs? Later on you write that there are some SSD optimizations in > > place that cut down idling already. > > It will have a functional difference even on SSDs, depending on your > workload, even if the scope of idling is smaller on an SSD. >>From 5414ce9fd8c384a3a25a478490a022539694e4e0 Mon Sep 17 00:00:00 2001 From: Martin Steigerwald Date: Mon, 28 Nov 2011 16:10:32 +0100 Subject: [PATCH 1/3] Mention that I/O priorities also work on direct writes. --- Documentation/block/ioprio.txt | 9 +++++---- 1 files changed, 5 insertions(+), 4 deletions(-) diff --git a/Documentation/block/ioprio.txt b/Documentation/block/ioprio.txt index 8ed8c59..a555c59 100644 --- a/Documentation/block/ioprio.txt +++ b/Documentation/block/ioprio.txt @@ -6,10 +6,11 @@ Intro ----- With the introduction of cfq v3 (aka cfq-ts or time sliced cfq), basic io -priorities are supported for reads on files. This enables users to io nice -processes or process groups, similar to what has been possible with cpu -scheduling for ages. This document mainly details the current possibilities -with cfq; other io schedulers do not support io priorities thus far. +priorities are supported for reads and direct, not buffered, writes on files +This enables users to io nice processes or process groups, similar to what +has been possible with cpu scheduling for ages. This document mainly details +the current possibilities with cfq; other io schedulers do not support io +priorities thus far. Scheduling classes ------------------ -- 1.7.7.3 Thanks, -- Martin Steigerwald - teamix GmbH - http://www.teamix.de gpg: 19E3 8D42 896F D004 08AC A0CA 1E10 C593 0399 AE90