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
