On Tue, Jul 8, 2014 at 9:07 PM, Christian Borntraeger
<borntrae...@de.ibm.com> wrote:
> On 08/07/14 19:08, Paolo Bonzini wrote:
>> Il 08/07/2014 17:59, Stefan Hajnoczi ha scritto:
>>> I sent Christian an initial patch to fix this but now both threads are
>>> stuck in rfifolock_lock() inside cond wait. That's very strange and
>>> should never happen.
>>
>> I had this patch pending for 2.2:
>>
>> commit 6c81e31615c3cda5ea981a998ba8b1b8ed17de6f
>> Author: Paolo Bonzini <pbonz...@redhat.com>
>> Date: Mon Jul 7 10:39:49 2014 +0200
>>
>> iothread: do not rely on aio_poll(ctx, true) result to end a loop
>>
>> Currently, whenever aio_poll(ctx, true) has completed all pending
>> work it returns true *and* the next call to aio_poll(ctx, true)
>> will not block.
>>
>> This invariant has its roots in qemu_aio_flush()'s implementation
>> as "while (qemu_aio_wait()) {}". However, qemu_aio_flush() does
>> not exist anymore and bdrv_drain_all() is implemented differently;
>> and this invariant is complicated to maintain and subtly different
>> from the return value of GMainLoop's g_main_context_iteration.
>>
>> All calls to aio_poll(ctx, true) except one are guarded by a
>> while() loop checking for a request to be incomplete, or a
>> BlockDriverState to be idle. Modify that one exception in
>> iothread.c.
>>
>> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
>
> The hangs are gone. Looks like 2.1 material now...
>
> Acked-by: Christian Borntraeger <borntrae...@de.ibm.com>
> Tested-by: Christian Borntraeger <borntrae...@de.ibm.com>
>
>
>
>
>>
>> diff --git a/iothread.c b/iothread.c
>> index 1fbf9f1..d9403cf 100644
>> --- a/iothread.c
>> +++ b/iothread.c
>> @@ -30,6 +30,7 @@ typedef ObjectClass IOThreadClass;
>> static void *iothread_run(void *opaque)
>> {
>> IOThread *iothread = opaque;
>> + bool blocking;
>>
>> qemu_mutex_lock(&iothread->init_done_lock);
>> iothread->thread_id = qemu_get_thread_id();
>> @@ -38,8 +39,10 @@ static void *iothread_run(void *opaque)
>>
>> while (!iothread->stopping) {
>> aio_context_acquire(iothread->ctx);
>> - while (!iothread->stopping && aio_poll(iothread->ctx, true)) {
>> + blocking = true;
>> + while (!iothread->stopping && aio_poll(iothread->ctx, blocking)) {
>> /* Progress was made, keep going */
>> + blocking = false;
>> }
>> aio_context_release(iothread->ctx);
>> }
>>
>> Christian, can you test it?
Could affect performance because of the extra poll/release/acquire but
a clean solution for broken iothread_run().
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
Good for 2.1
