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

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Message-ID: <CAMj5BkiMcsDsp+XvG3-zDVK2iWy-L0JvL2kcnAi7JkSeBzjpGQ@mail.gmail.com>
Date:   Wed, 16 Nov 2016 09:41:16 +0800
From:   Zhangfei Gao <zhangfei.gao@...il.com>
To:     John Garry <john.garry@...wei.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 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.

>
> 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>