On Sun, Oct 24, 2021 at 11:12:26AM +0300, Max Gurtovoy wrote:

On 10/24/2021 10:19 AM, Max Gurtovoy wrote:

quoted

On 10/22/2021 12:30 PM, Michael S. Tsirkin wrote:

quoted

On Thu, Sep 02, 2021 at 11:46:22PM +0300, Max Gurtovoy wrote:

quoted

Sometimes a user would like to control the amount of request queues to
be created for a block device. For example, for limiting the memory
footprint of virtio-blk devices.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
---

changes from v2:
  - renamed num_io_queues to num_request_queues (from Stefan)
  - added Reviewed-by signatures (from Stefan and Christoph)

changes from v1:
  - use param_set_uint_minmax (from Christoph)
  - added "Should > 0" to module description

Note: This commit apply on top of Jens's branch for-5.15/drivers

---
  drivers/block/virtio_blk.c | 21 ++++++++++++++++++++-
  1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 4b49df2dfd23..aaa2833a4734 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c

@@ -24,6 +24,23 @@

  /* The maximum number of sg elements that fit into a virtqueue */
  #define VIRTIO_BLK_MAX_SG_ELEMS 32768
  +static int virtblk_queue_count_set(const char *val,
+        const struct kernel_param *kp)
+{
+    return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
+}
+

BTW, I've noticed in your new message you allow setting 0 so you might want
to change the code to

param_set_uint_minmax(val, kp, 0, nr_cpu_ids);

to a case a user will load the module with num_request_queues=0.

Oh. So as written the default forces 1 queue?
Send a patch please!

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+static const struct kernel_param_ops queue_count_ops = {
+    .set = virtblk_queue_count_set,
+    .get = param_get_uint,
+};
+
+static unsigned int num_request_queues;
+module_param_cb(num_request_queues, &queue_count_ops,
&num_request_queues,
+        0644);
+MODULE_PARM_DESC(num_request_queues,
+         "Number of request queues to use for blk device.
Should > 0");
+
  static int major;
  static DEFINE_IDA(vd_index_ida);

I wasn't happy with the message here so I tweaked it.

Please look at it in linux-next and confirm. Thanks!

Looks good.

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@@ -501,7 +518,9 @@ static int init_vq(struct virtio_blk *vblk)

      if (err)
          num_vqs = 1;
  -    num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
+    num_vqs = min_t(unsigned int,
+            min_not_zero(num_request_queues, nr_cpu_ids),
+            num_vqs);
        vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs),
GFP_KERNEL);
      if (!vblk->vqs)
-- 
2.18.1