[Patch v3] storvsc: setup 1:1 mapping between hardware queue and CPU queue

[Patch v3] storvsc: setup 1:1 mapping between hardware queue and CPU queue

[longli]

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 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.

Changes:
v2: rely on default upper layer function to map queues. (suggested by Ming Lei
<tom.leiming@gmail.com>)
v3: use num_present_cpus() instead of num_online_cpus(). Hyper-v doesn't
support hot-add CPUs. (suggested by Michael Kelley <mikelley@microsoft.com>)

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..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();
 
 	/*
 	 * Set the error handler work queue.
-- 
2.17.1

RE: [Patch v3] storvsc: setup 1:1 mapping between hardware queue and CPU queue

[Michael Kelley]

From: Long Li <longli@microsoft.com> Sent: Thursday, September 5, 2019 3:55 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_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.
> 
> Changes:
> v2: rely on default upper layer function to map queues. (suggested by Ming Lei
> <tom.leiming@gmail.com>)
> v3: use num_present_cpus() instead of num_online_cpus(). Hyper-v doesn't
> support hot-add CPUs. (suggested by Michael Kelley <mikelley@microsoft.com>)

I've mostly seen the "Changes:" section placed below the "---" so that it doesn't
clutter up the commit log.  But maybe there's not a strong requirement one
way or the other as I didn't find anything called out in the "Documentation/process"
directory.

Michael

> 
> 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..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();
> 
>  	/*
>  	 * Set the error handler work queue.
> --
> 2.17.1

RE: [Patch v3] storvsc: setup 1:1 mapping between hardware queue and CPU queue

[Long Li]

>Subject: RE: [Patch v3] storvsc: setup 1:1 mapping between hardware queue
>and CPU queue
>
>From: Long Li <longli@microsoft.com> Sent: Thursday, September 5, 2019 3:55
>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_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.
>>
>> Changes:
>> v2: rely on default upper layer function to map queues. (suggested by
>> Ming Lei
>> <tom.leiming@gmail.com>)
>> v3: use num_present_cpus() instead of num_online_cpus(). Hyper-v
>> doesn't support hot-add CPUs. (suggested by Michael Kelley
>> <mikelley@microsoft.com>)
>
>I've mostly seen the "Changes:" section placed below the "---" so that it
>doesn't clutter up the commit log.  But maybe there's not a strong
>requirement one way or the other as I didn't find anything called out in the
>"Documentation/process"
>directory.

Should I resubmit the patch (but keep it v3)?

>
>Michael
>
>>
>> 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..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();
>>
>>  	/*
>>  	 * Set the error handler work queue.
>> --
>> 2.17.1

RE: [Patch v3] storvsc: setup 1:1 mapping between hardware queue and CPU queue

[Michael Kelley]

From: Long Li <longli@microsoft.com> Sent: Thursday, September 5, 2019 8:35 PM
> >>
> >> Changes:
> >> v2: rely on default upper layer function to map queues. (suggested by
> >> Ming Lei
> >> <tom.leiming@gmail.com>)
> >> v3: use num_present_cpus() instead of num_online_cpus(). Hyper-v
> >> doesn't support hot-add CPUs. (suggested by Michael Kelley
> >> <mikelley@microsoft.com>)
> >
> >I've mostly seen the "Changes:" section placed below the "---" so that it
> >doesn't clutter up the commit log.  But maybe there's not a strong
> >requirement one way or the other as I didn't find anything called out in the
> >"Documentation/process"
> >directory.
> 
> Should I resubmit the patch (but keep it v3)?
> 

I would say do a quick resubmit as v4 so there's no confusion.

Michael