From: Paolo Bonzini <pbonzini@redhat.com>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Kevin Wolf <kwolf@redhat.com>,
Anthony Liguori <aliguori@us.ibm.com>,
Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
Jan Kiszka <jan.kiszka@siemens.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
qemu-devel <qemu-devel@nongnu.org>, Avi Kivity <avi@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] Use qemu_eventfd for POSIX AIO
Date: Tue, 27 Sep 2011 16:41:44 +0200 [thread overview]
Message-ID: <4E81E0A8.20108@redhat.com> (raw)
In-Reply-To: <4E81D88B.4020504@codemonkey.ws>
On 09/27/2011 04:07 PM, Anthony Liguori wrote:
>
> I think it's a bit dangerous to implement eventfd() in terms of pipe().
>
> You don't expect to handle EAGAIN with eventfd() whereas you have to
> handle it with pipe().
>
> Moreover, the eventfd() counter is not lossy (practically speaking)
> whereas if you use pipe() as a counter, it will be lossy in practice.
>
> This is why posix aio uses pipe() and not eventfd().
But this is the same idiom we use for the iothread signaling. We're not
using the eventfd's counter. Perhaps it would be nice to complete
EventNotifier with "notify event" methods and use it, but Jan's patch is
safe, I think.
Paolo
prev parent reply other threads:[~2011-09-27 14:41 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <4E78C42D.5030207@siemens.com>
[not found] ` <20110921080600.GA9847@stefanha-thinkpad.localdomain>
[not found] ` <4E80B50B.9000301@siemens.com>
[not found] ` <4E80B55F.5020203@redhat.com>
[not found] ` <4E80BFF3.8000907@us.ibm.com>
[not found] ` <4E8190BE.3000801@redhat.com>
2011-09-27 13:56 ` [Qemu-devel] [PATCH] Use qemu_eventfd for POSIX AIO Jan Kiszka
2011-09-27 14:07 ` Anthony Liguori
2011-09-27 14:11 ` Avi Kivity
2011-09-27 14:19 ` Anthony Liguori
2011-09-27 14:22 ` Avi Kivity
2011-09-27 14:22 ` Jan Kiszka
2011-09-27 14:38 ` Anthony Liguori
2011-09-27 14:29 ` Jan Kiszka
2011-09-27 14:34 ` Avi Kivity
2011-09-27 14:36 ` Jan Kiszka
2011-09-27 14:42 ` Avi Kivity
2011-09-27 14:45 ` Jan Kiszka
2011-09-27 14:48 ` Avi Kivity
2011-09-27 14:50 ` Jan Kiszka
2011-09-27 14:54 ` Avi Kivity
2011-09-27 14:57 ` Anthony Liguori
2011-09-27 14:59 ` Jan Kiszka
2011-09-27 14:36 ` Anthony Liguori
2011-09-27 14:41 ` Paolo Bonzini [this message]
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