>Subject: Re: [Patch v4] storvsc: setup 1:1 mapping between hardware queue >and CPU queue > >On Fri, Sep 06, 2019 at 10:24:20AM -0700, longli@xxxxxxxxxxxxxxxxx wrote: >>From: Long Li <longli@xxxxxxxxxxxxx> >> >>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_present_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. >> >>Signed-off-by: Long Li <longli@xxxxxxxxxxxxx> >>--- >> >>Changes: >>v2: rely on default upper layer function to map queues. (suggested by >>Ming Lei >><tom.leiming@xxxxxxxxx>) >>v3: use num_present_cpus() instead of num_online_cpus(). Hyper-v >>doesn't support hot-add CPUs. (suggested by Michael Kelley >><mikelley@xxxxxxxxxxxxx>) >>v4: move change logs to after Signed-of-by >> >> 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..cf987712041a 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_present_cpus(); > >Just looking at the change notes for v3: why isn't this >num_active_cpus() then? One can still isolate CPUs on hyper-v, no? The isolated CPU can be made online at run time. For example, even maxcpus=x is put on the boot line, individual CPUs can still be made online/offline. > >-- >Thanks, >Sasha
