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Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation
From: |
Christoph Hellwig |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation |
Date: |
Wed, 27 Jul 2011 21:57:19 +0200 |
User-agent: |
Mutt/1.5.17 (2007-11-01) |
On Wed, Jul 27, 2011 at 09:52:51PM +0200, Frediano Ziglio wrote:
> >
>
> Yes! Not at kernel level :-)
In that case we have a bad error handling problem somewhere in qemu.
the IOCB_CMD_FDSYNC aio opcode will always return EINVAL currently,
and we really should have cought that somewhere in qemu.
> Thanks. I'll try to port misaligned access to Linux AIO. Also I'll add some
> comments on code to avoid somebody do the same mistache I did.
It's direct I/O code in general that doesn't handle misaligned access.
Given that we should never get misaligned I/O from guests I just didn't
bother duplicating the read-modify-write code for that code path as well.
> Mainly however -k qemu-img and aio=native in blockdev options are silently
> ignored if nocache is not enabled.
Maybe we should indeed error out instead. Care to prepare a patch for that?
> Also I notice that combining XFS, Linux AIO, O_DIRECT and O_DSYNC give
> impressive performance but currently there is no way to specify all that
> flags together cause nocache enable O_DIRECT while O_DSYNC is enabled with
> writethrough.
Indeed. This has come up a few times, and actually is a mostly trivial
task. Maybe we should give up waiting for -blockdev and separate cache
mode settings and allow a nocache-writethrough or similar mode now? It's
going to be around 10 lines of code + documentation.
- [Qemu-devel] [PATCH 0/2] improve Linux AIO support, Frediano Ziglio, 2011/07/27
- [Qemu-devel] [PATCH 1/2] linux aio: support flush operation, Frediano Ziglio, 2011/07/27
- Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation, Christoph Hellwig, 2011/07/27
- Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation, Frediano Ziglio, 2011/07/27
- Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation,
Christoph Hellwig <=
- Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation, Kevin Wolf, 2011/07/28
- Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation, Christoph Hellwig, 2011/07/28
- Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation, Kevin Wolf, 2011/07/28
- Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation, Christoph Hellwig, 2011/07/29
- Re: [Qemu-devel] [PATCH 1/2] linux aio: support flush operation, Stefan Hajnoczi, 2011/07/29
[Qemu-devel] [PATCH 2/2] aio: use Linux AIO even if nocache is not specified, Frediano Ziglio, 2011/07/27