From: Matthias Schniedermeyer <ms@citd.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: Michael Monnerie <michael.monnerie@is.it-management.at>, xfs@oss.sgi.com
Subject: Re: [PATCH] xfs_repair: multithread phase 2
Date: Mon, 10 Jan 2011 22:53:51 +0100 [thread overview]
Message-ID: <20110110215351.GA26675@citd.de> (raw)
In-Reply-To: <20110110191757.GA25029@infradead.org>
On 10.01.2011 14:17, Christoph Hellwig wrote:
> On Mon, Jan 10, 2011 at 07:41:22PM +1100, Dave Chinner wrote:
> > On Mon, Jan 10, 2011 at 08:57:52AM +0100, Michael Monnerie wrote:
> > > On Montag, 10. Januar 2011 Dave Chinner wrote:
> > > > This patch uses 32-way threading which results in no noticable
> > > > slowdown on single SATA drives with NCQ, but results in ~10x
> > > > reduction in runtime on a 12 disk RAID-0 array.
> > >
> > > Is the fixed 32-way number reasonable, or shouldn't that be "number of
> > > available cpu cores"-way? Why threading when you have a single core cpu?
> >
> > Sure, 32-way is reasonable on a single disk and CPU. Pretty much
> > every sata disk supports NCQ these days, and default to a depth of
> > 32, which means we can have 32 concurrent reads in progress at once.
> > Phase 2 is all synchronous IO, so the only way to hide the IO
> > latency is to queue work to multiple threads and switch between the
> > threadsto work on another queue when the current one blocks waiting
> > for IO.
>
> The default queue depth for ATA NCQ actually is 31, not 32 for some odd
> reason.
AFAIR the original discussion it's because Depth 0 and 32 use the same
value. And the knowledge that (HDD-)firmware tends to be buggy, so it
was decided to stay on the safe side and not use "0/32".
Bis denn
--
Real Programmers consider "what you see is what you get" to be just as
bad a concept in Text Editors as it is in women. No, the Real Programmer
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next prev parent reply other threads:[~2011-01-10 21:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-10 0:44 [PATCH] xfs_repair: multithread phase 2 Dave Chinner
2011-01-10 7:57 ` Michael Monnerie
2011-01-10 8:41 ` Dave Chinner
2011-01-10 13:25 ` Michael Monnerie
2011-01-10 19:18 ` Christoph Hellwig
2011-01-10 19:17 ` Christoph Hellwig
2011-01-10 21:53 ` Matthias Schniedermeyer [this message]
2011-01-10 18:55 ` Christoph Hellwig
2011-02-01 23:39 ` Alex Elder
-- strict thread matches above, loose matches on Subject: below --
2011-01-04 6:13 Dave Chinner
2011-01-04 10:02 ` Christoph Hellwig
2011-01-04 12:00 ` Dave Chinner
2011-01-05 23:42 ` Alex Elder
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