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

[Paolo Bonzini]

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.

Paolo