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

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Date:   Wed, 16 Nov 2016 10:02:47 +0000
From:   John Garry <john.garry@...wei.com>
To:     Zhangfei Gao <zhangfei.gao@...il.com>
CC:     <martin.petersen@...cle.com>, <jejb@...ux.vnet.ibm.com>,
        <linux-scsi@...r.kernel.org>, <linuxarm@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        John Garry <john.garry2@...l.dcu.ie>,
        Xiang Chen <chenxiang66@...ilicon.com>
Subject: Re: [PATCH 02/11] hisi_sas: alloc queue id of slot according to
 device id

On 16/11/2016 01:41, Zhangfei Gao wrote:
> On Mon, Nov 7, 2016 at 8:48 PM, John Garry <john.garry@...wei.com> wrote:
>> From: Xiang Chen <chenxiang66@...ilicon.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@...ilicon.com>
>> Signed-off-by: John Garry <john.garry@...wei.com>
>
> Reviewed-by: Zhangfei Gao <zhangfei.gao@...aro.org>
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