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

On Tue, Aug 20, 2019 at 3:36 AM [off-list ref] wrote:

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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,

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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)

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        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;
+       }

Block layer provides the helper of blk_mq_map_queues(), so suggest you
to use the default cpu mapping, instead of inventing a new one.

Thanks for the pointer. I'm sending a v2.

Long

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thanks,
Ming Lei