virtio-blk: base queue-depth on virtqueue ringsize or module param
Venkatash spake thus: virtio-blk set the default queue depth to 64 requests, which was insufficient for high-IOPS devices. Instead set the blk-queue depth to the device's virtqueue depth divided by two (each I/O requires at least two VQ entries). But behold, Ted added a module parameter: Also allow the queue depth to be something which can be set at module load time or via a kernel boot-time parameter, for testing/benchmarking purposes. And I rewrote it substantially, mainly to take VIRTIO_RING_F_INDIRECT_DESC into account. As QEMU sets the vq size for PCI to 128, Venkatash's patch wouldn't have made a change. This version does (since QEMU also offers VIRTIO_RING_F_INDIRECT_DESC. Inspired-by:"Theodore Ts'o" <tytso@mit.edu> Based-on-the-true-story-of: Venkatesh Srinivas <venkateshs@google.com> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: virtio-dev@lists.oasis-open.org Cc: virtualization@lists.linux-foundation.org Cc: Frank Swiderski <fes@google.com> Signed-off-by:
Rusty Russell <rusty@rustcorp.com.au>
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