RE: [Patch v2] storvsc: setup 1:1 mapping between hardware queue and CPU queue
From: Michael Kelley <hidden>
Date: 2019-08-22 21:01:38
Also in:
linux-scsi, lkml
From: Long Li <redacted> Sent: Thursday, August 22, 2019 1:42 PM
quoted hunk ↗ jump to hunk
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_possible_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 [off-list ref]) Signed-off-by: Long Li <longli@microsoft.com> --- 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..dfd3b76a4f89 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_possible_cpus();
For a lot of the VM sizes in Azure, num_possible_cpus() is 128, even if the VM has only 4 or 8 or some other smaller number of vCPUs. So I'm wondering if you really want num_present_cpus() here instead, which would include only the vCPUs that actually exist in the VM. Michael
/* * Set the error handler work queue. -- 2.17.1