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Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT)
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT) |
Date: |
Wed, 30 Apr 2008 01:02:19 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Kevin Wolf wrote:
> Disabling O_DIRECT for a single aio request is impossible (after all,
> aio is asynchronous), and disabling it for at least one aio request is
> going to be ugly.
You could try opening two fds to the same file/blockdev, one with
O_DIRECT set. Then you can disable O_DIRECT as you like per aio
request, by choosing the fd.
I'm not sure if that works, though. On some OSes, if a file has any
non-O_DIRECT open descriptor, all I/O is buffered ignoring the
O_DIRECT flag. If both are allowed simultaneously, I'm not sure what
happens with cache-coherency between direct I/Os and buffered I/Os.
-- Jamie
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), (continued)
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Kevin Wolf, 2008/04/29
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Laurent Vivier, 2008/04/29
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Kevin Wolf, 2008/04/29
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Laurent Vivier, 2008/04/29
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Kevin Wolf, 2008/04/30
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Laurent Vivier, 2008/04/30
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Kevin Wolf, 2008/04/30
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Blue Swirl, 2008/04/30
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Kevin Wolf, 2008/04/30
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT), Jamie Lokier, 2008/04/29
- Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT),
Jamie Lokier <=