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

[Zhi Yong Wu]

On Fri, Apr 13, 2012 at 3:18 PM, Paolo Bonzini <address@hidden> wrote:
> 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:
Sorry, i hadn't check the code. thanks for pointing out this. In the
past, i tested this patch, and found it will assert about
bs->tracked_requests. Do you think that only qemu_aio_wait can make
sure that bs->tracked_requests is empty here?
>
>>> +
>>> +        /* 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
>>>
>>>
>>>
>>
>>
>>
>
>
>



-- 
Regards,

Zhi Yong Wu