From: Jens Axboe <qemu@kernel.dk> To: Andrea Arcangeli <aarcange@redhat.com> Cc: Jens Axboe <qemu@kernel.dk>, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>, kvm-devel <kvm@vger.kernel.org> Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool Date: Fri, 12 Dec 2008 12:54:21 +0100 [thread overview] Message-ID: <20081212115420.GR23742@kernel.dk> (raw) In-Reply-To: <20081212115133.GI6809@random.random> On Fri, Dec 12 2008, Andrea Arcangeli wrote: > On Fri, Dec 12, 2008 at 09:23:10AM +0100, Jens Axboe wrote: > > aio is only async with O_DIRECT, with buffered IO it's sync. > > That's very bad, because aio is as needed for O_DIRECT as for buffered > read seeking workloads that otherwise have zero chance to fill the > I/O pipe... (well unless one is threading in userland which is obviously > less efficient than what aio could achieve in kernel space, even I agree completely. The buffered aio patches got pretty involved though, it wasn't real pretty in the end. So it never got merged. Looks like the most realistic way forward is some variant of syslet (or the acall stuff that Zach has been working on), which is largely a cop out and will never perform as well. > without taking cfq screwed bucketing into account). I added CLONE_IO some time ago to avoid that, so it's perfectly possible to share cfq io contexts with threads or processes even in userspace! -- Jens Axboe
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From: Jens Axboe <qemu@kernel.dk> To: Andrea Arcangeli <aarcange@redhat.com> Cc: qemu-devel@nongnu.org, kvm-devel <kvm@vger.kernel.org>, Gerd Hoffmann <kraxel@redhat.com> Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool Date: Fri, 12 Dec 2008 12:54:21 +0100 [thread overview] Message-ID: <20081212115420.GR23742@kernel.dk> (raw) In-Reply-To: <20081212115133.GI6809@random.random> On Fri, Dec 12 2008, Andrea Arcangeli wrote: > On Fri, Dec 12, 2008 at 09:23:10AM +0100, Jens Axboe wrote: > > aio is only async with O_DIRECT, with buffered IO it's sync. > > That's very bad, because aio is as needed for O_DIRECT as for buffered > read seeking workloads that otherwise have zero chance to fill the > I/O pipe... (well unless one is threading in userland which is obviously > less efficient than what aio could achieve in kernel space, even I agree completely. The buffered aio patches got pretty involved though, it wasn't real pretty in the end. So it never got merged. Looks like the most realistic way forward is some variant of syslet (or the acall stuff that Zach has been working on), which is largely a cop out and will never perform as well. > without taking cfq screwed bucketing into account). I added CLONE_IO some time ago to avoid that, so it's perfectly possible to share cfq io contexts with threads or processes even in userspace! -- Jens Axboe
next prev parent reply other threads:[~2008-12-12 11:54 UTC|newest] Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-12-05 21:21 [RFC] Replace posix-aio with custom thread pool Anthony Liguori 2008-12-05 21:21 ` [Qemu-devel] " Anthony Liguori 2008-12-06 9:03 ` Blue Swirl 2008-12-06 18:26 ` Jamie Lokier 2008-12-08 18:23 ` Anthony Liguori 2008-12-08 18:23 ` Anthony Liguori 2008-12-09 15:51 ` Gerd Hoffmann 2008-12-09 16:01 ` Anthony Liguori 2008-12-10 16:44 ` Andrea Arcangeli 2008-12-10 17:21 ` Anthony Liguori 2008-12-10 17:21 ` Anthony Liguori 2008-12-10 17:29 ` Gerd Hoffmann 2008-12-10 18:50 ` Anthony Liguori 2008-12-10 19:08 ` Andrea Arcangeli 2008-12-10 19:08 ` Andrea Arcangeli 2008-12-11 13:12 ` Andrea Arcangeli 2008-12-11 15:24 ` Gerd Hoffmann 2008-12-11 15:24 ` Gerd Hoffmann 2008-12-11 15:53 ` Andrea Arcangeli 2008-12-11 15:53 ` Andrea Arcangeli 2008-12-11 16:11 ` Gerd Hoffmann 2008-12-11 16:11 ` Gerd Hoffmann 2008-12-11 16:49 ` Andrea Arcangeli 2008-12-11 16:49 ` Andrea Arcangeli 2008-12-11 17:20 ` Gerd Hoffmann 2008-12-11 17:20 ` Gerd Hoffmann 2008-12-11 18:11 ` Andrea Arcangeli 2008-12-11 18:11 ` Andrea Arcangeli 2008-12-11 20:38 ` Gerd Hoffmann 2008-12-11 20:38 ` Gerd Hoffmann 2008-12-11 20:40 ` Anthony Liguori 2008-12-12 8:23 ` Jens Axboe 2008-12-12 8:23 ` Jens Axboe 2008-12-12 11:51 ` Andrea Arcangeli 2008-12-12 11:51 ` Andrea Arcangeli 2008-12-12 11:54 ` Jens Axboe [this message] 2008-12-12 11:54 ` Jens Axboe 2008-12-12 14:13 ` Andrea Arcangeli 2008-12-12 14:13 ` Andrea Arcangeli 2008-12-12 14:24 ` Anthony Liguori 2008-12-12 14:24 ` Anthony Liguori 2008-12-12 16:33 ` Chris Wright 2008-12-12 16:33 ` Chris Wright 2008-12-12 16:51 ` Anthony Liguori 2008-12-12 16:51 ` Anthony Liguori 2008-12-12 16:52 ` Chris Wright 2008-12-12 16:52 ` Chris Wright 2008-12-11 21:32 ` Christoph Hellwig 2008-12-12 0:27 ` Andrea Arcangeli 2008-12-12 0:27 ` Andrea Arcangeli 2008-12-11 21:30 ` Christoph Hellwig 2008-12-11 16:41 ` Anthony Liguori 2008-12-11 16:41 ` Anthony Liguori 2008-12-12 14:24 ` Andrea Arcangeli 2008-12-12 14:24 ` Andrea Arcangeli 2008-12-12 14:35 ` Anthony Liguori 2008-12-12 14:35 ` Anthony Liguori 2008-12-12 15:44 ` Andrea Arcangeli 2008-12-12 15:44 ` Andrea Arcangeli 2008-12-12 16:49 ` Anthony Liguori 2008-12-12 16:49 ` Anthony Liguori 2008-12-12 17:09 ` Andrea Arcangeli 2008-12-12 17:09 ` Andrea Arcangeli 2008-12-12 17:25 ` Anthony Liguori 2008-12-12 17:25 ` Anthony Liguori 2008-12-12 17:52 ` Andrea Arcangeli 2008-12-12 17:52 ` Andrea Arcangeli 2008-12-12 18:17 ` Anthony Liguori 2008-12-12 18:17 ` Anthony Liguori 2008-12-12 18:26 ` Andrea Arcangeli 2008-12-12 20:12 ` Gerd Hoffmann 2008-12-12 20:17 ` Anthony Liguori 2008-12-12 20:35 ` Gerd Hoffmann 2008-12-09 17:16 ` Avi Kivity 2008-12-17 14:44 ` Ian Jackson
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