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* [Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue
@ 2019-09-06 17:24 longli
  2019-09-06 19:14 ` Michael Kelley
  2019-09-06 20:08 ` Sasha Levin
  0 siblings, 2 replies; 4+ messages in thread
From: longli @ 2019-09-06 17:24 UTC (permalink / raw)
  To: K. Y. Srinivasan, Haiyang Zhang, Stephen Hemminger, Sasha Levin,
	James E.J. Bottomley, Martin K. Petersen, linux-hyperv,
	linux-scsi, linux-kernel
  Cc: Long Li

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.

Signed-off-by: Long Li <longli@microsoft.com>
---

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


^ permalink raw reply	[flat|nested] 4+ messages in thread

* RE: [Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue
  2019-09-06 17:24 [Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue longli
@ 2019-09-06 19:14 ` Michael Kelley
  2019-09-06 20:08 ` Sasha Levin
  1 sibling, 0 replies; 4+ messages in thread
From: Michael Kelley @ 2019-09-06 19:14 UTC (permalink / raw)
  To: longli, KY Srinivasan, Haiyang Zhang, Stephen Hemminger,
	Sasha Levin, James E.J. Bottomley, Martin K. Petersen,
	linux-hyperv, linux-scsi, linux-kernel
  Cc: Long Li

From: Long Li <longli@microsoft.com> Sent: Friday, September 6, 2019 10:24 AM
> 
> 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@microsoft.com>
> ---
> 
> 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>)
> 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();
> 
>  	/*
>  	 * Set the error handler work queue.
> --
> 2.17.1

Reviewed-by: Michael Kelley <mikelley@microsoft.com>


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue
  2019-09-06 17:24 [Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue longli
  2019-09-06 19:14 ` Michael Kelley
@ 2019-09-06 20:08 ` Sasha Levin
  2019-09-06 21:37   ` Long Li
  1 sibling, 1 reply; 4+ messages in thread
From: Sasha Levin @ 2019-09-06 20:08 UTC (permalink / raw)
  To: longli
  Cc: K. Y. Srinivasan, Haiyang Zhang, Stephen Hemminger,
	James E.J. Bottomley, Martin K. Petersen, linux-hyperv,
	linux-scsi, linux-kernel, Long Li

On Fri, Sep 06, 2019 at 10:24:20AM -0700, longli@linuxonhyperv.com wrote:
>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.
>
>Signed-off-by: Long Li <longli@microsoft.com>
>---
>
>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>)
>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?

--
Thanks,
Sasha

^ permalink raw reply	[flat|nested] 4+ messages in thread

* RE: [Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue
  2019-09-06 20:08 ` Sasha Levin
@ 2019-09-06 21:37   ` Long Li
  0 siblings, 0 replies; 4+ messages in thread
From: Long Li @ 2019-09-06 21:37 UTC (permalink / raw)
  To: Sasha Levin, longli
  Cc: KY Srinivasan, Haiyang Zhang, Stephen Hemminger,
	James E.J. Bottomley, Martin K. Petersen, linux-hyperv,
	linux-scsi, linux-kernel

>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@linuxonhyperv.com wrote:
>>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.
>>
>>Signed-off-by: Long Li <longli@microsoft.com>
>>---
>>
>>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>)
>>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

^ permalink raw reply	[flat|nested] 4+ messages in thread

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2019-09-06 17:24 [Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue longli
2019-09-06 19:14 ` Michael Kelley
2019-09-06 20:08 ` Sasha Levin
2019-09-06 21:37   ` Long Li

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