Messages in this thread Patch in this message | | | From | Martin Steigerwald <> | Subject | [PATCH 3/3] Mention that the util-linux package provides an ionice command. | Date | Mon, 28 Nov 2011 16:24:33 +0100 |
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Am Montag, 28. November 2011 schrieb Martin Steigerwald: > 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? > > > 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.
And mentioned that ionice is available from the util-linux package:
From 182d2e06d65ea784c2bbf2e756ce0452fdebef8c Mon Sep 17 00:00:00 2001 From: Martin Steigerwald <ms@teamix.de> Date: Mon, 28 Nov 2011 16:16:33 +0100 Subject: [PATCH 3/3] Mention that the util-linux package provides an ionice command.
--- Documentation/block/ioprio.txt | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/Documentation/block/ioprio.txt b/Documentation/block/ioprio.txt index 4775a95..5b79a29 100644 --- a/Documentation/block/ioprio.txt +++ b/Documentation/block/ioprio.txt @@ -58,6 +58,9 @@ For a running process, you can give the pid instead: will change pid 100 to run at the realtime scheduling class, at priority 2. +The util-linux package includes an ionice command that basically works like +described here. + ---> snip ionice.c tool <--- #include <stdio.h> -- 1.7.7.3 Thanks, -- Martin Steigerwald - teamix GmbH - http://www.teamix.de gpg: 19E3 8D42 896F D004 08AC A0CA 1E10 C593 0399 AE90
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