* [Patch v2] storvsc: setup 1:1 mapping between hardware queue and CPU queue
@ 2019-08-22 20:42 longli
2019-08-22 21:01 ` Michael Kelley
0 siblings, 1 reply; 4+ messages in thread
From: longli @ 2019-08-22 20:42 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_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@gmail.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..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();
/*
* Set the error handler work queue.
--
2.17.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* RE: [Patch v2] storvsc: setup 1:1 mapping between hardware queue and CPU queue
2019-08-22 20:42 [Patch v2] storvsc: setup 1:1 mapping between hardware queue and CPU queue longli
@ 2019-08-22 21:01 ` Michael Kelley
2019-08-22 22:21 ` Long Li
0 siblings, 1 reply; 4+ messages in thread
From: Michael Kelley @ 2019-08-22 21:01 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@linuxonhyperv.com> 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@gmail.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..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.
Michael
>
> /*
> * Set the error handler work queue.
> --
> 2.17.1
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [Patch v2] storvsc: setup 1:1 mapping between hardware queue and CPU queue
2019-08-22 21:01 ` Michael Kelley
@ 2019-08-22 22:21 ` Long Li
2019-08-22 22:29 ` Long Li
0 siblings, 1 reply; 4+ messages in thread
From: Long Li @ 2019-08-22 22:21 UTC (permalink / raw)
To: Michael Kelley, longli, KY Srinivasan, Haiyang Zhang,
Stephen Hemminger, Sasha Levin, James E.J. Bottomley,
Martin K. Petersen, linux-hyperv, linux-scsi, linux-kernel
>>>Subject: RE: [Patch v2] storvsc: setup 1:1 mapping between hardware
>>>queue and CPU queue
>>>
>>>From: Long Li <longli@linuxonhyperv.com> 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@gmail.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..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
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [Patch v2] storvsc: setup 1:1 mapping between hardware queue and CPU queue
2019-08-22 22:21 ` Long Li
@ 2019-08-22 22:29 ` Long Li
0 siblings, 0 replies; 4+ messages in thread
From: Long Li @ 2019-08-22 22:29 UTC (permalink / raw)
To: Michael Kelley, longli, KY Srinivasan, Haiyang Zhang,
Stephen Hemminger, Sasha Levin, James E.J. Bottomley,
Martin K. Petersen, linux-hyperv, linux-scsi, linux-kernel
>>>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@linuxonhyperv.com> 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@gmail.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..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
^ permalink raw reply [flat|nested] 4+ messages in thread
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2019-08-22 20:42 [Patch v2] storvsc: setup 1:1 mapping between hardware queue and CPU queue longli
2019-08-22 21:01 ` Michael Kelley
2019-08-22 22:21 ` Long Li
2019-08-22 22:29 ` Long Li
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