>>>Subject: RE: [Patch v2] storvsc: setup 1:1 mapping between hardware >>>queue and CPU queue >>> >>>From: Long Li <longli@xxxxxxxxxxxxxxxxx> Sent: Thursday, August 22, 2019 >>>1:42 PM >>>> >>>> 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 >>>> <tom.leiming@xxxxxxxxx>) >>>> >>>> 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..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. I think reporting num_possible_cpus() doesn't do more harm or take more resources. Because block layer allocates map for all the possible CPUs. The actual mapping is done in blk_mq_map_queues(), and it iterates all the possible CPUs. If we report num_present_cpus(), the rest of the CPUs also need to be mapped. >>> >>>Michael >>> >>>> >>>> /* >>>> * Set the error handler work queue. >>>> -- >>>> 2.17.1
