Re: [PATCH RFC] virtio-blk: support per-device queue depth

[Jason Wang <jasowang@redhat.com>]

On 2021/1/19 上午9:33, JeffleXu wrote:
>
> On 1/18/21 1:25 PM, Jason Wang wrote:
>> On 2021/1/18 上午11:58, Joseph Qi wrote:
>>> module parameter 'virtblk_queue_depth' was firstly introduced for
>>> testing/benchmarking purposes described in commit fc4324b4597c
>>> ("virtio-blk: base queue-depth on virtqueue ringsize or module param").
>>> Since we have different virtio-blk devices which have different
>>> capabilities, it requires that we support per-device queue depth instead
>>> of per-module. So defaultly use vq free elements if module parameter
>>> 'virtblk_queue_depth' is not set.
>>
>> I wonder if it's better to use sysfs instead (or whether it has already
>> had something like this in the blocker layer).
>>
> "/sys/block/<dev>/queue/nr_requests" indeed works, but isn't better to
> set queue_depth according to the hardware capability at the very first?
> AFAIK, nvme just set per-device queue_depth at initializing phase.


I agree, the problem is that the current code may modify module parameter.

Thanks


>
> Thanks,
> Jeffle
>
>>
>>> Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
>>> ---
>>>    drivers/block/virtio_blk.c | 12 +++++++-----
>>>    1 file changed, 7 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>> index 145606d..f83a417 100644
>>> --- a/drivers/block/virtio_blk.c
>>> +++ b/drivers/block/virtio_blk.c
>>> @@ -705,6 +705,7 @@ static int virtblk_probe(struct virtio_device *vdev)
>>>        u32 v, blk_size, max_size, sg_elems, opt_io_size;
>>>        u16 min_io_size;
>>>        u8 physical_block_exp, alignment_offset;
>>> +    unsigned int queue_depth;
>>>          if (!vdev->config->get) {
>>>            dev_err(&vdev->dev, "%s failure: config access disabled\n",
>>> @@ -755,17 +756,18 @@ static int virtblk_probe(struct virtio_device
>>> *vdev)
>>>            goto out_free_vq;
>>>        }
>>>    -    /* Default queue sizing is to fill the ring. */
>>> -    if (!virtblk_queue_depth) {
>>> -        virtblk_queue_depth = vblk->vqs[0].vq->num_free;
>>> +    if (likely(!virtblk_queue_depth)) {
>>> +        queue_depth = vblk->vqs[0].vq->num_free;
>>>            /* ... but without indirect descs, we use 2 descs per req */
>>>            if (!virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC))
>>> -            virtblk_queue_depth /= 2;
>>> +            queue_depth /= 2;
>>> +    } else {
>>> +        queue_depth = virtblk_queue_depth;
>>>        }
>>>          memset(&vblk->tag_set, 0, sizeof(vblk->tag_set));
>>>        vblk->tag_set.ops = &virtio_mq_ops;
>>> -    vblk->tag_set.queue_depth = virtblk_queue_depth;
>>> +    vblk->tag_set.queue_depth = queue_depth;
>>>        vblk->tag_set.numa_node = NUMA_NO_NODE;
>>>        vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
>>>        vblk->tag_set.cmd_size =