On Tue, Sep 27, 2011 at 10:23 PM, Anthony Liguori <anth...@codemonkey.ws> wrote: > On 09/27/2011 11:39 AM, Paolo Bonzini wrote: >> >> 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. > > Bottom halves are signal safe, not thread safe. > > To make bottom halves thread safe, you would (in the very least) have to add > some barriers when reading/writing the scheduling flag. I think it's much > better to just use GIdle sources though. > >>> 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? :) > > The sync I/O emulation. Since sync I/O is done in block drivers, they can > just use coroutine I/O instead of sync I/O.
Yes, I think we should covert sync I/O code to use coroutines, which is quite natural. The users of sync I/O today are: 1. Hardware emulation - lesser-used or not performance-critical code paths still use bdrv_read/write() in places, e.g. sd, nand, fdc, ide pio. 2. Block drivers. Some image formats are synchronous, but converting to coroutines is pretty easy. 3. qemu-tools including qemu-img and qemu-io. With Paolo's work to make the event loop available in qemu-tools it should be possible to convert and eliminate synchronous I/O interfaces. Stefan
