queue-4.19/virtio-blk-limit-number-of-hw-queues-by-nr_cpu_ids.patch

   1 From 24ca25647f542d987e27df551901e4ada72c6400 Mon Sep 17 00:00:00 2001
   2 From: Dongli Zhang <dongli.zhang@oracle.com>
   3 Date: Wed, 27 Mar 2019 18:36:34 +0800
   4 Subject: virtio-blk: limit number of hw queues by nr_cpu_ids
   5
   6 [ Upstream commit bf348f9b78d413e75bb079462751a1d86b6de36c ]
   7
   8 When tag_set->nr_maps is 1, the block layer limits the number of hw queues
   9 by nr_cpu_ids. No matter how many hw queues are used by virtio-blk, as it
  10 has (tag_set->nr_maps == 1), it can use at most nr_cpu_ids hw queues.
  11
  12 In addition, specifically for pci scenario, when the 'num-queues' specified
  13 by qemu is more than maxcpus, virtio-blk would not be able to allocate more
  14 than maxcpus vectors in order to have a vector for each queue. As a result,
  15 it falls back into MSI-X with one vector for config and one shared for
  16 queues.
  17
  18 Considering above reasons, this patch limits the number of hw queues used
  19 by virtio-blk by nr_cpu_ids.
  20
  21 Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
  22 Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
  23 Signed-off-by: Jens Axboe <axboe@kernel.dk>
  24 Signed-off-by: Sasha Levin <sashal@kernel.org>
  25 ---
  26  drivers/block/virtio_blk.c | 2 ++
  27  1 file changed, 2 insertions(+)
  28
  29 diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
  30 index 23752dc99b008..dd64f586679e1 100644
  31 --- a/drivers/block/virtio_blk.c
  32 +++ b/drivers/block/virtio_blk.c
  33 @@ -446,6 +446,8 @@ static int init_vq(struct virtio_blk *vblk)
  34         if (err)
  35                 num_vqs = 1;
  36
  37 +       num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
  38 +
  39         vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
  40         if (!vblk->vqs)
  41                 return -ENOMEM;
  42 --
  43 2.20.1
  44