linux-kernel - Re: [PATCH] drivers: virtio_blk: notify blk-core when hw-queue number changes

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Date:	Thu, 28 Jul 2016 16:18:08 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, mst@...hat.com
Subject: Re: [PATCH] drivers: virtio_blk: notify blk-core when hw-queue number
 changes


On 06/19/2016 06:10 AM, Paolo Bonzini wrote:
> 
> 
> On 13/06/2016 11:58, Bob Liu wrote:
>> A guest might be migrated to other hosts with different num_queues, the
>> blk-core should aware of that else the reference of &vblk->vqs[qid] may be wrong.
>>
>> Signed-off-by: Bob Liu <bob.liu@...cle.com>
>> ---
>>  drivers/block/virtio_blk.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>> index 42758b5..c169238 100644
>> --- a/drivers/block/virtio_blk.c
>> +++ b/drivers/block/virtio_blk.c
>> @@ -819,6 +819,9 @@ static int virtblk_restore(struct virtio_device *vdev)
>>  	if (ret)
>>  		return ret;
>>  
>> +	if (vblk->num_vqs != vblk->tag_set.nr_hw_queues)
>> +		blk_mq_update_nr_hw_queues(&vblk->tag_set, vblk->num_vqs);
>> +
>>  	virtio_device_ready(vdev);
>>  
>>  	blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
>>
> 
> This should never happen; it'd be a configuration problem.
> 

Do you mean all hosts have to be configured with the same number of ->num_vqs?
What about cases like migrating a guest from HostA to HostB while HostB is much more powerful
and would like to run more hardware queues to get better performance.

Thanks,
Bob Liu