Jan and Alex have expressed that aio_poll(ctx, blocking=true) should block even
when there are no file descriptors registered. This can be handy since other
threads may still kick the AioContext using aio_notify(ctx).
A concrete example is a thread that has only a timer in its AioContext.
aio_poll(ctx, true) should block until the timer expires or another thread
invokes aio_notify(ctx).
Alex and Paolo were concerned about bdrv_drain_all() which has the following
comment:
while (busy) {
/* FIXME: We do not have timer support here, so this is effectively
* a busy wait.
*/
QTAILQ_FOREACH(bs, &bdrv_states, list) {
if (bdrv_start_throttled_reqs(bs)) {
busy = true;
}
}
busy = bdrv_requests_pending_all();
busy |= aio_poll(qemu_get_aio_context(), busy);
}
Patch 1 drops this outdated comment. The new I/O throttling code already
eliminated the busy wait.
Patch 2 drops the special case which returns immediately from aio_poll(ctx,
true) when no file descriptors are registered.
Note that aio_notify(ctx) still causes aio_poll(ctx, true) to return false. I
don't see a need to change it so aio_poll(ctx, true) always returns true.
Stefan Hajnoczi (2):
block: clean up bdrv_drain_all() throttling comments
aio: make aio_poll(ctx, true) block with no fds
aio-posix.c | 5 -----
aio-win32.c | 5 -----
block.c | 7 +------
tests/test-aio.c | 1 -
4 files changed, 1 insertion(+), 17 deletions(-)
--
1.8.3.1
