Messages in this thread Patch in this message | | | Date | Wed, 30 Nov 2011 16:01:11 +0100 (CET) | From | Martin Steigerwald <> | Subject | Re: [PATCH 1/1] Mention that I/O priorities also work on direct writes. |
| |
Hi Jens!
Did you notice the three patches I send?
Thanks, Martin
----- Ursprüngliche Mail ----- > 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 <ms@teamix.de> > 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 > -- > 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/ >
-- Martin Steigerwald Trainer / Consultant
teamix GmbH Solide IT-Infrastruktur Südwestpark 35 90449 Nürnberg
fon: +49 (911) 30999- 0 fax: +49 (911) 30999-99 mail: ms@teamix.de web: http://www.teamix.de vcf: http://www.teamix.de/vcf/ms.vcf gpg: 19E3 8D42 896F D004 08AC A0CA 1E10 C593 0399 AE90
Amtsgericht Nürnberg, HRB 18320 Geschäftsführer: Oliver Kügow, Richard Müller -- 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/
| |