From: Phillip Susi <psusi@cfl.rr.com>
To: Denis Vlasenko <vda.linux@googlemail.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>,
Linus Torvalds <torvalds@osdl.org>, Viktor <vvp01@inbox.ru>,
Aubrey <aubreylee@gmail.com>, Hua Zhong <hzhong@gmail.com>,
Hugh Dickins <hugh@veritas.com>,
linux-kernel@vger.kernel.org, hch@infradead.org,
kenneth.w.chen@in
Subject: Re: O_DIRECT question
Date: Fri, 26 Jan 2007 12:05:50 -0500 [thread overview]
Message-ID: <45BA34EE.4050402@cfl.rr.com> (raw)
In-Reply-To: <200701252211.39017.vda.linux@googlemail.com>
Denis Vlasenko wrote:
> Which shouldn't be true. There is no fundamental reason why
> ordinary writes should be slower than O_DIRECT.
Again, there IS a reason: O_DIRECT eliminates the cpu overhead of the
kernel-user copy, and when coupled with multithreading or aio, allows
the IO queues to be kept full with useful transfers at all times.
Normal read/write requires the kernel to buffer and guess access
patterns correctly to perform read ahead and write behind perfectly to
keep the queues full. In practice, this does not happen perfectly all
of the time, or even most of the time, so it slows things down.
next prev parent reply other threads:[~2007-01-26 17:05 UTC|newest]
Thread overview: 130+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-11 2:57 O_DIRECT question Aubrey
2007-01-11 3:05 ` Linus Torvalds
2007-01-11 3:15 ` Linus Torvalds
2007-01-11 6:09 ` Nick Piggin
2007-01-11 15:50 ` Linus Torvalds
2007-01-11 16:19 ` Aubrey
2007-01-16 3:41 ` Jörn Engel
2007-01-11 16:23 ` bert hubert
2007-01-11 16:52 ` Xavier Bestel
2007-01-11 17:04 ` Linus Torvalds
2007-01-11 18:41 ` Trond Myklebust
2007-01-11 19:00 ` Linus Torvalds
2007-01-11 19:49 ` Trond Myklebust
2007-01-12 17:03 ` Viktor
2007-01-20 16:19 ` Denis Vlasenko
2007-01-22 15:52 ` Phillip Susi
2007-01-11 5:50 ` Aubrey
2007-01-11 6:06 ` Andrew Morton
2007-01-11 6:45 ` Aubrey
2007-01-11 6:57 ` Andrew Morton
2007-01-11 7:05 ` Nick Piggin
2007-01-11 7:54 ` Aubrey
2007-01-11 8:05 ` Roy Huang
2007-01-11 16:45 ` Linus Torvalds
2007-01-17 4:29 ` Aubrey Li
2007-01-12 2:12 ` Aubrey
2007-01-12 2:47 ` Nick Piggin
2007-01-12 3:59 ` Roy Huang
2007-01-11 8:12 ` Nick Piggin
2007-01-11 8:49 ` Roy Huang
2007-01-11 9:09 ` Nick Piggin
2007-01-12 2:48 ` Bill Davidsen
2007-01-12 4:30 ` Nick Piggin
2007-01-12 4:46 ` Linus Torvalds
2007-01-12 4:56 ` Nick Piggin
2007-01-12 4:58 ` Nick Piggin
2007-01-12 5:18 ` Linus Torvalds
2007-01-12 5:22 ` Aubrey
2007-01-12 14:59 ` Bill Davidsen
2007-01-13 4:51 ` Nick Piggin
2007-01-11 6:16 ` Alexander Shishkin
2007-01-11 6:57 ` Aubrey
2007-01-11 12:13 ` Viktor
2007-01-11 15:53 ` Phillip Susi
2007-01-11 16:20 ` Linus Torvalds
2007-01-11 17:13 ` Michael Tokarev
2007-01-11 23:01 ` Phillip Susi
2007-01-11 23:06 ` Hua Zhong
2007-01-12 15:21 ` Phillip Susi
2007-01-20 16:36 ` Denis Vlasenko
2007-01-20 20:55 ` Michael Tokarev
2007-01-20 23:05 ` Denis Vlasenko
2007-01-21 12:09 ` Michael Tokarev
2007-01-21 20:02 ` Denis Vlasenko
2007-01-22 16:17 ` Phillip Susi
2007-01-24 21:15 ` Denis Vlasenko
2007-01-25 15:44 ` Phillip Susi
2007-01-25 17:38 ` Denis Vlasenko
2007-01-25 19:28 ` Phillip Susi
2007-01-25 19:52 ` Denis Vlasenko
2007-01-25 20:03 ` Phillip Susi
2007-01-25 20:45 ` Michael Tokarev
2007-01-25 21:11 ` Denis Vlasenko
2007-01-26 16:02 ` Mark Lord
2007-01-26 16:52 ` Viktor
2007-01-26 16:58 ` Phillip Susi
2007-01-26 17:05 ` Phillip Susi [this message]
2007-01-26 23:16 ` Denis Vlasenko
2007-02-06 20:39 ` Pavel Machek
2007-01-26 18:23 ` Bill Davidsen
2007-01-26 23:35 ` Denis Vlasenko
2007-01-28 15:18 ` Bill Davidsen
2007-01-28 17:03 ` Denis Vlasenko
2007-01-29 15:43 ` Phillip Susi
2007-01-29 17:00 ` Andrea Arcangeli
2007-01-30 0:05 ` Denis Vlasenko
[not found] ` <45BE7D99.70200@cfl.rr.com>
[not found] ` <20070130023056.GN8030@opteron.random>
[not found] ` <45BF65E3.6070102@cfl.rr.com>
[not found] ` <20070130164806.GQ8030@opteron.random>
2007-01-30 18:50 ` Phillip Susi
2007-01-30 19:57 ` Andrea Arcangeli
2007-01-30 20:06 ` Andrea Arcangeli
2007-01-30 23:07 ` Phillip Susi
2007-01-31 2:28 ` Andrea Arcangeli
2007-01-31 9:37 ` Michael Tokarev
2007-01-26 15:53 ` Bill Davidsen
2007-01-11 17:42 ` Alan
2007-01-11 18:00 ` Linus Torvalds
2007-01-12 7:57 ` dean gaudet
2007-01-12 15:27 ` Phillip Susi
2007-01-12 18:06 ` Linus Torvalds
2007-01-12 20:23 ` Chris Mason
2007-01-12 20:46 ` Michael Tokarev
2007-01-12 20:52 ` Michael Tokarev
2007-01-12 21:03 ` Michael Tokarev
2007-01-12 21:17 ` Linus Torvalds
2007-01-12 21:54 ` Michael Tokarev
2007-01-12 22:09 ` Linus Torvalds
2007-01-12 22:26 ` Michael Tokarev
2007-01-12 22:35 ` Erik Andersen
2007-01-12 22:47 ` Andrew Morton
2007-01-14 9:11 ` Nate Diller
2007-01-20 16:45 ` Denis Vlasenko
2007-01-22 1:47 ` Andrea Arcangeli
2007-01-13 20:07 ` Bill Davidsen
2007-01-13 20:27 ` Michael Tokarev
2007-01-14 15:39 ` Bill Davidsen
2007-01-12 21:39 ` Disk Cache, Was: " Zan Lynx
2007-01-12 22:10 ` Michael Tokarev
2007-01-15 12:11 ` Helge Hafting
2007-01-12 16:59 ` Viktor
2007-01-11 12:45 ` Erik Mouw
2007-01-11 4:51 ` Andrew Morton
2007-01-11 5:06 ` Gerrit Huizenga
2007-01-11 16:09 ` Badari Pulavarty
2007-01-11 12:34 ` linux-os (Dick Johnson)
2007-01-11 13:06 ` Martin Mares
2007-01-11 14:15 ` Jens Axboe
2007-01-12 2:13 ` Bill Davidsen
-- strict thread matches above, loose matches on Subject: below --
2007-01-17 14:27 Alex Tomas
2007-01-22 15:59 Al Boldi
[not found] <7BYkO-5OV-17@gated-at.bofh.it>
[not found] ` <7BYul-6gz-5@gated-at.bofh.it>
[not found] ` <7C18X-1zo-5@gated-at.bofh.it>
[not found] ` <7C1iw-22q-7@gated-at.bofh.it>
[not found] ` <7C1Vb-2Ny-3@gated-at.bofh.it>
[not found] ` <7C256-2ZR-27@gated-at.bofh.it>
[not found] ` <7C2eE-3rT-15@gated-at.bofh.it>
[not found] ` <7C31d-4qb-11@gated-at.bofh.it>
[not found] ` <7C3kj-55E-9@gated-at.bofh.it>
2007-01-11 13:20 ` Bodo Eggert
[not found] ` <7C74B-2A4-23@gated-at.bofh.it>
[not found] ` <7CaYA-mT-19@gated-at.bofh.it>
[not found] ` <7Cpuz-64X-1@gated-at.bofh.it>
[not found] ` <7Cz0T-4PH-17@gated-at.bofh.it>
[not found] ` <7CBcl-86B-9@gated-at.bofh.it>
[not found] ` <7CBvH-52-9@gated-at.bofh.it>
[not found] ` <7CBFn-hw-1@gated-at.bofh.it>
[not found] ` <7CBP1-KI-3@gated-at.bofh.it>
[not found] ` <7CBYG-WK-3@gated-at.bofh.it>
2007-01-13 16:53 ` Bodo Eggert
2007-01-13 19:30 ` Bill Davidsen
2007-01-14 18:51 ` Bodo Eggert
[not found] ` <7CXmz-88G-29@gated-at.bofh.it>
[not found] ` <7CXFR-8vZ-15@gated-at.bofh.it>
[not found] ` <7DfMP-2ak-19@gated-at.bofh.it>
2007-01-14 19:39 ` Bodo Eggert
[not found] ` <7DyYK-6lE-3@gated-at.bofh.it>
2007-01-16 20:26 ` Bodo Eggert
2007-01-17 5:55 ` Arjan van de Ven
2007-01-17 22:36 ` Bodo Eggert
[not found] ` <7HkaQ-2Nb-9@gated-at.bofh.it>
[not found] ` <7HDZP-Pv-1@gated-at.bofh.it>
[not found] ` <7HIPV-8kp-35@gated-at.bofh.it>
2007-01-27 14:01 ` Bodo Eggert
2007-01-27 14:14 ` Denis Vlasenko
2007-01-28 15:30 ` Bill Davidsen
2007-01-28 17:18 ` Denis Vlasenko
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