>>>Subject: RE: [Patch v2] storvsc: setup 1:1 mapping between hardware >>>queue and CPU queue >>> >>>>>>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. Actually I get your point, reporting num_present_cpus() will get less number of struct blk_mq_hw_ctx created. So it saves memory. If we don't plan to support adding/onlining CPUs, we should use num_present_cpus(). >>> >>>>>> >>>>>>Michael >>>>>> >>>>>>> >>>>>>> /* >>>>>>> * Set the error handler work queue. >>>>>>> -- >>>>>>> 2.17.1
