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From:   Ming Lei <tom.leiming@gmail.com>
Date:   Sat, 11 Jan 2020 20:08:09 +0800
Message-ID: <CACVXFVOJnDG9HTxdHMKjttHkVsu+12LmbO9+AAU5+TrFYhAz_w@mail.gmail.com>
Subject: Re: [PATCH] scsi: storvsc: Correctly set number of hardware queues
 for IDE disk
To:     longli@linuxonhyperv.com
Cc:     "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Sasha Levin <sashal@kernel.org>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-hyperv@vger.kernel.org,
        Linux SCSI List <linux-scsi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Long Li <longli@microsoft.com>
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On Sat, Jan 11, 2020 at 4:17 PM <longli@linuxonhyperv.com> wrote:
>
> From: Long Li <longli@microsoft.com>
>
> Commit 0ed881027690 ("scsi: storvsc: setup 1:1 mapping between hardware queue and CPU queue")
> introduced a regression for disks attached to IDE. For these disks the host VSP only offers
> one VMBUS channel. Setting multiple queues can overload the VMBUS channel and result in
> performance drop for high queue depth workload on system with large number of CPUs.
>
> Fix it by leaving the number of hardware queues to 1 (default value) for IDE
> disks.
>
> Fixes: 0ed881027690 ("scsi: storvsc: setup 1:1 mapping between hardware queue and CPU queue")
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
>  drivers/scsi/storvsc_drv.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index f8faf8b3d965..992b28e40374 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -1842,9 +1842,11 @@ static int storvsc_probe(struct hv_device *device,
>          */
>         host->sg_tablesize = (stor_device->max_transfer_bytes >> PAGE_SHIFT);
>         /*
> +        * For non-IDE disks, the host supports multiple channels.
>          * Set the number of HW queues we are supporting.
>          */
> -       host->nr_hw_queues = num_present_cpus();
> +       if (dev_id->driver_data != IDE_GUID)
> +               host->nr_hw_queues = num_present_cpus();
>
>         /*
>          * Set the error handler work queue.
> --
> 2.20.1
>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

-- 
Ming Lei