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

[longli@linuxonhyperv.com]

From: Long Li <longli@microsoft.com>

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 sets up a 1:1 mapping between hardware queue and CPU queue, thus
avoiding unnecessary locking at upper layer when issuing I/O.

Signed-off-by: Long Li <longli@microsoft.com>
---
 drivers/scsi/storvsc_drv.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index b89269120a2d..26c16d40ec46 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1682,6 +1682,18 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
 	return 0;
 }
 
+static int storvsc_map_queues(struct Scsi_Host *shost)
+{
+	unsigned int cpu;
+	struct blk_mq_queue_map *qmap = &shost->tag_set.map[HCTX_TYPE_DEFAULT];
+
+	for_each_possible_cpu(cpu) {
+		qmap->mq_map[cpu] = cpu;
+	}
+
+	return 0;
+}
+
 static struct scsi_host_template scsi_driver = {
 	.module	=		THIS_MODULE,
 	.name =			"storvsc_host_t",
@@ -1697,6 +1709,7 @@ static struct scsi_host_template scsi_driver = {
 	.this_id =		-1,
 	/* Make sure we dont get a sg segment crosses a page boundary */
 	.dma_boundary =		PAGE_SIZE-1,
+	.map_queues =		storvsc_map_queues,
 	.no_write_same =	1,
 	.track_queue_depth =	1,
 };
@@ -1836,8 +1849,7 @@ 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_possible_cpus();
 
 	/*
 	 * Set the error handler work queue.
-- 
2.17.1