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Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf,
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier) |
Date: |
Wed, 7 May 2008 17:26:42 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Kevin Wolf wrote:
> No, nobody mentioned the recursion problem.
Hmm. I concede you're right in the sense that it was mentioned, but
on a different thread about QEMU AIO recently :-)
Message-ID: <address@hidden>
Avi Kivity wrote:
> Long term we want to replace the recursion by queuing.
Ah yes. Reminds me of a bug in a program of mine with asynchronous
sockets.
<explanation of bug>
I learned a few lessons about async callbacks:
<general advice>
> And you were talking about
> problem with two different file descriptors for one file, not about the
> fcntl solution. Ok, might also be that the hints were just not explicit
> enough for me. ;-)
Following the paragraph about two file descriptors, there was:
>> 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.
Not sure if that is quite the same thing :-)
I did miss that switching O_DIRECT on/off while AIOs are in flight on
that descriptor might be dodgy (implementation dependent), and that it
might not do the right things w.r.t. cohrency.
> But even if so, this is more of a general feeling about how patches are
> handled and not only related to this patch.
I agree and have a similar feeling, though it's not a bad thing
provided the issues are actually noticed, which they do seem to be. I
have the impression there are many people working on different
specific features and subsystems, but not so much on overall
architecture in a coordinated and "visionary" way.
Most of my issues with QEMU are the epic list of difficulties with
Microsoft guests (espcially when people send me images for a different
VM), the peculiar divergence between KVM and QEMU features, and the
awkwardness of the monitor/command line interface. Since I'm not an
active code contributor, and those are to a great extent feature
requests or only debuggable by users, I keep those thoughts largely to
myself :-)
-- Jamie
- [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Blue Swirl, 2008/05/06
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Fabrice Bellard, 2008/05/06
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Anthony Liguori, 2008/05/06
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Jamie Lokier, 2008/05/07
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Kevin Wolf, 2008/05/07
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Jamie Lokier, 2008/05/07
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Kevin Wolf, 2008/05/07
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Blue Swirl, 2008/05/07
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Kevin Wolf, 2008/05/07
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier),
Jamie Lokier <=
- Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier), Kevin Wolf, 2008/05/07