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Re: [PATCH 02/11] hisi_sas: alloc queue id of slot according to device id

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  Re: [PATCH 02/11] hisi_sas: alloc queue id of slot according to  device id Zhangfei Gao <zhangfei.gao@gmail.com> - 2016-11-16 02:50 +0100
    Re: [PATCH 02/11] hisi_sas: alloc queue id of slot according to  device id John Garry <john.garry@huawei.com> - 2016-11-16 11:10 +0100

#1523178 — Re: [PATCH 02/11] hisi_sas: alloc queue id of slot according to device id

On Mon, Nov 7, 2016 at 8:48 PM, John Garry <john.garry@huawei.com> wrote:
> From: Xiang Chen <chenxiang66@hisilicon.com>
>
> Currently slots are allocated from queues in a round-robin fashion.
> This causes a problem for internal commands in device mode. For this
> mode, we should ensure that the internal abort command is the last
> command seen in the host for that device. We can only ensure this when
> we place the internal abort command after the preceding commands for
> device that in the same queue, as there is no order in which the host
> will select a queue to execute the next command.

Is there performance penalty, since only one queue is supported for a device.

>
> This queue restriction makes supporting scsi mq more tricky in
> the future, but should not be a blocker.
>
> Note: Even though v1 hw does not support internal abort, the
>       allocation method is chosen to be the same for consistency.
>
> Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
> Signed-off-by: John Garry <john.garry@huawei.com>

Reviewed-by: Zhangfei Gao <zhangfei.gao@linaro.org>

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#1523349

On 16/11/2016 01:41, Zhangfei Gao wrote:
> On Mon, Nov 7, 2016 at 8:48 PM, John Garry <john.garry@huawei.com> wrote:
>> From: Xiang Chen <chenxiang66@hisilicon.com>
>>
>> Currently slots are allocated from queues in a round-robin fashion.
>> This causes a problem for internal commands in device mode. For this
>> mode, we should ensure that the internal abort command is the last
>> command seen in the host for that device. We can only ensure this when
>> we place the internal abort command after the preceding commands for
>> device that in the same queue, as there is no order in which the host
>> will select a queue to execute the next command.
>
> Is there performance penalty, since only one queue is supported for a device.

Hi Zhangfei,

 From testing I have not seen any noteable performance change. However, 
please note the comment on mq, below.

Cheers,
John

>
>>
>> This queue restriction makes supporting scsi mq more tricky in
>> the future, but should not be a blocker.
>>
>> Note: Even though v1 hw does not support internal abort, the
>>       allocation method is chosen to be the same for consistency.
>>
>> Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
>> Signed-off-by: John Garry <john.garry@huawei.com>
>
> Reviewed-by: Zhangfei Gao <zhangfei.gao@linaro.org>
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