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SubjectRe: [RESEND PATCH] xen/blkfront: convert to blk-mq APIs

On 07/11/2015 03:57 AM, Konrad Rzeszutek Wilk wrote:
> On Mon, Jul 06, 2015 at 05:56:48PM +0800, Bob Liu wrote:
>> From: Arianna Avanzini <avanzini.arianna@gmail.com>
>>
>> This patch converts xen-blkfront driver to use the block multiqueue APIs.
>> Only one hardware queue is used now, so there is no performance change.
>>
>> The legacy non-mq code was deleted completely which is the same as other drivers
>> like virtio, mtip, and nvme.
>>
>> Also dropped unnecessary holding of info->io_lock when calling into blk-mq APIs.
>
> Yeey!
>
> Two points:
>
> - The io_lock is now used to guard against concurrent access to the ring.
> We should rename it to 'ring_lock'.
>

Sure.

> - The kick_pending_request_queues should have an extra argument - 'bool locked'.
> This is so that you don't drop and immediately grab the lock from the blkif_interrupt.
>

Then where to drop the lock?

In kick_pending_request_queues(), the lock have to be dropped before calling blk_mq_start_stopped_hw_queues().

static void kick_pending_request_queues(struct blkfront_info *info)
{
+ unsigned long flags;
+
+ spin_lock_irqsave(&info->io_lock, flags);
if (!RING_FULL(&info->ring)) {
- /* Re-enable calldowns. */
- blk_start_queue(info->rq);
- /* Kick things off immediately. */
- do_blkif_request(info->rq);
+ spin_unlock_irqrestore(&info->io_lock, flags);
+ blk_mq_start_stopped_hw_queues(info->rq, true);
+ return;
}

> See:
>
>> @@ -1243,9 +1243,8 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>> } else
>> info->ring.sring->rsp_event = i + 1;
>>
>> - kick_pending_request_queues(info);
>> -
>> spin_unlock_irqrestore(&info->io_lock, flags);
>> + kick_pending_request_queues(info);
>>
>> return IRQ_HANDLED;
>> }
>
> Otherwise Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>

--
Regards,
-Bob


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