Re: [Qemu-devel] [PATCH 07/26] block: add the support to drain throttled requests

[Paolo Bonzini]

Il 13/04/2012 03:55, Zhi Yong Wu ha scritto:
> On Thu, Apr 12, 2012 at 8:00 PM, Paolo Bonzini <address@hidden> wrote:
>> From: Zhi Yong Wu <address@hidden>
>>
>> Signed-off-by: Zhi Yong Wu <address@hidden>
>> [ Iterate until all block devices have processed all requests,
>>  add comments. - Paolo ]
>> Signed-off-by: Paolo Bonzini <address@hidden>
>> ---
>>  block.c |   21 ++++++++++++++++++++-
>>  1 file changed, 20 insertions(+), 1 deletion(-)
>>
>> diff --git a/block.c b/block.c
>> index 4b96654..33efa95 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -863,12 +863,31 @@ void bdrv_close_all(void)
>>  *
>>  * This function does not flush data to disk, use bdrv_flush_all() for that
>>  * after calling this function.
>> + *
>> + * Note that completion of an asynchronous I/O operation can trigger any
>> + * number of other I/O operations on other devices---for example a coroutine
>> + * can be arbitrarily complex and a constant flow of I/O can come until the
>> + * coroutine is complete.  Because of this, it is not possible to have a
>> + * function to drain a single device's I/O queue.
>>  */
>>  void bdrv_drain_all(void)
>>  {
>>     BlockDriverState *bs;
>> +    bool busy;
>>
>> -    qemu_aio_flush();
>> +    do {
>> +        busy = qemu_aio_wait();
> When bdrv_drain_all is invoked, if bs->tracked_requests has some
> pending I/O requests, only qemu_aio_wait is called here, not
> qemu_aio_flush() to restart them in bs->tracked_requests. It will
> cause assert about bs->tracked_requests.

qemu_aio_flush does not do that.  Instead, the code just below does it:

>> +
>> +        /* FIXME: We do not have timer support here, so this is effectively
>> +         * a busy wait.
>> +         */
>> +        QTAILQ_FOREACH(bs, &bdrv_states, list) {
>> +            if (!qemu_co_queue_empty(&bs->throttled_reqs)) {
>> +                qemu_co_queue_restart_all(&bs->throttled_reqs);
>> +                busy = true;
>> +            }
>> +        }
>> +    } while (busy);
>>
>>     /* If requests are still pending there is a bug somewhere */
>>     QTAILQ_FOREACH(bs, &bdrv_states, list) {
>> --
>> 1.7.9.3
>>
>>
>>
> 
> 
>