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Re: [Qemu-devel] Re: [PATCH 06/13] Threadlet: Add dequeue_work threadlet
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] Re: [PATCH 06/13] Threadlet: Add dequeue_work threadlet API |
Date: |
Fri, 7 Jan 2011 11:06:16 +0000 |
On Thu, Jan 6, 2011 at 10:43 AM, Arun R Bharadwaj
<address@hidden> wrote:
> * Stefan Hajnoczi <address@hidden> [2011-01-05 19:55:46]:
>
>> On Tue, Jan 04, 2011 at 10:57:39AM +0530, Arun R Bharadwaj wrote:
>> > @@ -574,33 +574,39 @@ static void paio_remove(struct qemu_paiocb *acb)
>> > }
>> > }
>> >
>> > -static void paio_cancel(BlockDriverAIOCB *blockacb)
>> > +/**
>> > + * dequeue_work: Cancel a task queued on the global queue.
>> > + * @work: Contains the information of the task that needs to be cancelled.
>> > + *
>> > + * Returns: 0 if the task is successfully cancelled.
>> > + * 1 otherwise.
>> > + */
>> > +static int dequeue_work(ThreadletWork *work)
>> > {
>> > - struct qemu_paiocb *acb = (struct qemu_paiocb *)blockacb;
>> > - int active = 0;
>> > + int ret = 1;
>> >
>> > qemu_mutex_lock(&globalqueue.lock);
>> > - if (!acb->active) {
>> > - QTAILQ_REMOVE(&globalqueue.request_list, &acb->work, node);
>> > - acb->ret = -ECANCELED;
>> > - } else if (acb->ret == -EINPROGRESS) {
>> > - active = 1;
>> > - }
>> > + QTAILQ_REMOVE(&globalqueue.request_list, work, node);
>> > + ret = 0;
>> > qemu_mutex_unlock(&globalqueue.lock);
>> >
>> > - qemu_mutex_lock(&aiocb_mutex);
>> > - if (!active) {
>> > - acb->ret = -ECANCELED;
>> > - } else {
>> > - while (acb->ret == -EINPROGRESS) {
>> > - /*
>> > - * fail safe: if the aio could not be canceled,
>> > - * we wait for it
>> > - */
>> > - qemu_cond_wait(&aiocb_completion, &aiocb_mutex);
>> > + return ret;
>>
>> It always succeeds? Why bother with the ret local variable?
>>
>
> Yes, I'll remove this.
>
>> > +}
>> > +
>> > +static void paio_cancel(BlockDriverAIOCB *blockacb)
>> > +{
>> > + struct qemu_paiocb *acb = (struct qemu_paiocb *)blockacb;
>> > + if (!acb->active) {
>> > + if (dequeue_work(&acb->work) != 0) {
>> > + /* Wait for running work item to complete */
>> > + qemu_mutex_lock(&aiocb_mutex);
>> > + while (acb->ret == -EINPROGRESS) {
>> > + qemu_cond_wait(&aiocb_completion, &aiocb_mutex);
>> > + }
>> > + qemu_mutex_unlock(&aiocb_mutex);
>> > }
>> > }
>> > - qemu_mutex_unlock(&aiocb_mutex);
>> > +
>> > paio_remove(acb);
>>
>> I'm not convinced this function works. If the request is active in a
>> worker thread and paio_cancel() is called then we invoke paio_remove().
>>
>
> True. So can we do this: Since we have a patch which separately
> removes the active field [PATCH 7/13], can we fold patch 7 and this
> patch into a single patch? So that way we can maintain the
> correctness, because we are actually waiting for the active work to
> complete by doing a while (acb->ret == -EINPROGRESS)
Sounds good. IIRC the paio_cancel() code in the last version of the
patch looked correct, so it probably *is* just a case of not splitting
this part up into separate patches.
Stefan
- [Qemu-devel] [PATCH 03/13] Add callback function to ThreadletWork structure., (continued)
- [Qemu-devel] [PATCH 07/13] Remove active field in qemu_aiocb structure., Arun R Bharadwaj, 2011/01/04
- [Qemu-devel] [PATCH 08/13] Remove thread_create routine., Arun R Bharadwaj, 2011/01/04
- [Qemu-devel] [PATCH 09/13] Threadlet: Add aio_signal_handler threadlet API, Arun R Bharadwaj, 2011/01/04
- [Qemu-devel] [PATCH 10/13] Remove all instances of CONFIG_THREAD, Arun R Bharadwaj, 2011/01/04
- [Qemu-devel] [PATCH 11/13] Move threadlet code to qemu-threadlets.c, Arun R Bharadwaj, 2011/01/04
- [Qemu-devel] [PATCH 12/13] Threadlets: Add functionality to create private queues., Arun R Bharadwaj, 2011/01/04
- [Qemu-devel] [PATCH 13/13] Threadlets: Add documentation, Arun R Bharadwaj, 2011/01/04
- Re: [Qemu-devel] [PATCH 00/13] Threadlets infrastructure., Venkateswararao Jujjuri (JV), 2011/01/04