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Subject[Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue
From: Long Li <>

storvsc doesn't use a dedicated hardware queue for a given CPU queue. When
issuing I/O, it selects returning CPU (hardware queue) dynamically based on
vmbus channel usage across all channels.

This patch advertises num_present_cpus() as number of hardware queues. This
will have upper layer setup 1:1 mapping between hardware queue and CPU queue
and avoid unnecessary locking when issuing I/O.

Signed-off-by: Long Li <>

v2: rely on default upper layer function to map queues. (suggested by Ming Lei
v3: use num_present_cpus() instead of num_online_cpus(). Hyper-v doesn't
support hot-add CPUs. (suggested by Michael Kelley <>)
v4: move change logs to after Signed-of-by

drivers/scsi/storvsc_drv.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index b89269120a2d..cf987712041a 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1836,8 +1836,7 @@ static int storvsc_probe(struct hv_device *device,
* Set the number of HW queues we are supporting.
- if (stor_device->num_sc != 0)
- host->nr_hw_queues = stor_device->num_sc + 1;
+ host->nr_hw_queues = num_present_cpus();

* Set the error handler work queue.
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