[Patch v3] storvsc: setup 1:1 mapping between hardware queue and CPU queue

[longli]

From: Long Li <longli@xxxxxxxxxxxxx>

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.

Changes:
v2: rely on default upper layer function to map queues. (suggested by Ming Lei
<tom.leiming@xxxxxxxxx>)
v3: use num_present_cpus() instead of num_online_cpus(). Hyper-v doesn't
support hot-add CPUs. (suggested by Michael Kelley <mikelley@xxxxxxxxxxxxx>)

Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
---
 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.
-- 
2.17.1