From: Jens Axboe <email@example.com>
To: Ian Kumlien <firstname.lastname@example.org>
Cc: Ihar Philips Filipau <email@example.com>,
Linux Kernel Mailing List <firstname.lastname@example.org>
Subject: Re: [SHED][IO-SHED] Are we missing the big picture?
Date: Fri, 1 Aug 2003 14:32:36 +0200 [thread overview]
Message-ID: <20030801123236.GS7920@suse.de> (raw)
On Fri, Aug 01 2003, Ian Kumlien wrote:
> On Fri, 2003-08-01 at 11:00, Ihar "Philips" Filipau wrote:
> > Am I right - judging from your posting - that we finally reached
> > moment than Linux will have network-like queueing disciplines for disks
> > and CPUs?
> CPU's? well, we do have a nice sheduler but i wouldn't say network-like
> > In any way, CPU/disk throughput just another types of limited resource.
> > It would be nice to be able to manage it - who gets more, who gets
> > less. CPU/disk schedulers by manageability are far behind network.
> > IMHO must have for servers.
> Yes, but, thats not what I'm saying.
> CFQ as it apparently was called, builds a queue list when the disk is
I coined that phrase as a variant of SFQ, with C being Complete.
> under load. So you get really fast data access if there is no load, and
> a common queue when there is load. The common queue is the bad thing
> about CFQ, imagine putting AS there instead... This would mean fast data
> access on unloaded systems, better throughput on loaded systems and
> prioritization features could hook right in since AS would only be used
> during load. IE, you can add all kinds of patches that only matters
> during heavy load.
I dunno where you get this from, but you seem to have a misguide picture
of how io schedulers work in Linux. AS works like deadline, but adds
anticipation. This means you try to anticipate whether a process will
issue a nearby read soon, and if so stall the disk head. deadline itself
has a single queue for merging/sorting, and a single queue as a deadline
fifo (for each data direction, read and write).
Where CFQ differs is that it maintains such a backend system for each
"class" (user, could be a task grouping of some sort too), with a small
front end (class independent scheduler is used in some contexts) to
select which class we do IO from. The old design just round-robined
between all "busy" tasks, with some heuristics to minimize seeks.
So for a single task, deadline and CFQ works the same basically. AS
differs because of the anticipation of course.
> > > I liked Jens Axobe's 'CBQ' alike implementation (based on the idea of
> > > Andrea A. (afair i have the names right) since it does the most
Nope, it's Axboe :)
next prev parent reply other threads:[~2003-08-01 12:32 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <fw7N.3DP.email@example.com>
2003-08-01 9:00 ` [SHED][IO-SHED] Are we missing the big picture? Ihar "Philips" Filipau
2003-08-01 12:23 ` Ian Kumlien
2003-08-01 12:32 ` Jens Axboe [this message]
2003-08-01 13:01 ` Ian Kumlien
2003-08-01 0:32 Ian Kumlien
2003-08-01 6:27 ` Nick Piggin
2003-08-01 12:18 ` Ian Kumlien
2003-08-02 1:49 ` Nick Piggin
2003-08-02 2:07 ` Ian Kumlien
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