linux-kernel - Re: [RFC PATCH 2/2] block: virtio-blk: support multi virt queues per virtio-blk device

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Date:	Tue, 17 Jun 2014 23:50:57 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Stefan Hajnoczi <stefanha@...il.com>
Cc:	Jens Axboe <axboe@...nel.dk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>, linux-api@...r.kernel.org,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH 2/2] block: virtio-blk: support multi virt queues per
 virtio-blk device

On Tue, Jun 17, 2014 at 10:40 AM, Stefan Hajnoczi <stefanha@...il.com> wrote:
> On Sat, Jun 14, 2014 at 1:29 AM, Ming Lei <ming.lei@...onical.com> wrote:
>> Firstly this patch supports more than one virtual queues for virtio-blk
>> device.
>>
>> Secondly this patch maps the virtual queue to blk-mq's hardware queue.
>>
>> With this approach, both scalability and performance problem can be improved.
>>
>> Signed-off-by: Ming Lei <ming.lei@...onical.com>
>> ---
>>  drivers/block/virtio_blk.c |   75 ++++++++++++++++++++++++++++++++------------
>>  1 file changed, 55 insertions(+), 20 deletions(-)
>>
>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>> index f63d358..e0d077d 100644
>> --- a/drivers/block/virtio_blk.c
>> +++ b/drivers/block/virtio_blk.c
>> @@ -16,6 +16,8 @@
>>
>>  #define PART_BITS 4
>>
>> +#define MAX_NUM_VQ 16
>
> It would be nice to allocate virtqueues dynamically instead of
> hardcoding the limit.  virtio-scsi also allocates virtqueues
> dynamically.

virtio-scsi may have lots of LUN, but virtio-blk only has one disk
which needn't lots of hardware queues.

Also it doesn't matter since it isn't part of ABI.

If change on virtio_blk_config is agreed, both host side and
guest side can choose to support dynamic length or pre-defined
length freely.

Thanks,
--
Ming Lei
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