linux-kernel - RE: [Patch v4] storvsc: setup 1:1 mapping between hardware queue and CPU queue

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Date:   Tue, 24 Sep 2019 01:14:23 +0000
From:   Long Li <longli@...rosoft.com>
To:     Long Li <longli@...rosoft.com>, Sasha Levin <sashal@...nel.org>,
        "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Patch v4] storvsc: setup 1:1 mapping between hardware queue and
 CPU queue

>Subject: RE: [Patch v4] storvsc: setup 1:1 mapping between hardware queue
>and CPU queue
>
>>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@...uxonhyperv.com wrote:
>>>From: Long Li <longli@...rosoft.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@...rosoft.com>

Hi Martin,

I have addressed all comments on this patch. Can you merge it to SCSI?

If there is anything else I need to change, please let me know.

Thanks

Long


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