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Re: [Qemu-devel] [PATCH] event_notifier: move to top-level directory

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] event_notifier: move to top-level directory
Date: Tue, 27 Sep 2011 18:39:05 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2

On 09/27/2011 06:05 PM, Anthony Liguori wrote:
Actually, for posix-aio, we can just switch to using g_idle_add().
g_idle_add() uses g_source_attach which is thread safe.  g_idle_add()
 gives you a thread safe mechanism to defer a piece of work to the
main loop which is really what we want here.

For that, a bottom half would also do (apart that I am not sure it is
async-safe with TCG).  In fact, that would make sense since all of
posix_aio_process_queue could become a bottom half.

But the problem to be solved here is waking up qemu_aio_wait, and
scheduling bottom halves currently wakes up only the vl.c main loop.

This can actually be made to work with sync I/O emulation too by
having another GMainLoop in the sync I/O loop although I thought I
recalled a patch series to remove that stuff.

... which stuff? :) Another GMainLoop in the sync I/O loop is problematic for two reasons: 1) the sync I/O loop does not relinquish the I/O thread mutex, which makes it very different from the outer loop; 2) a nested GMainLoop keeps polling all the file descriptors in the outer loop, which requires you to cope with reentrancy in those monitor commands that flush AIO.


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