linux-kernel - Re: [PATCH V9 6/7] SCSI: allow to pass null rq to scsi_prep_state

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Date:   Fri, 13 Oct 2017 23:16:12 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "hch@...radead.org" <hch@...radead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "axboe@...com" <axboe@...com>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tom81094@...il.com" <tom81094@...il.com>,
        "paolo.valente@...aro.org" <paolo.valente@...aro.org>,
        Bart Van Assche <Bart.VanAssche@....com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "oleksandr@...alenko.name" <oleksandr@...alenko.name>,
        "john.garry@...wei.com" <john.garry@...wei.com>,
        "osandov@...com" <osandov@...com>,
        "loberman@...hat.com" <loberman@...hat.com>
Subject: Re: [PATCH V9 6/7] SCSI: allow to pass null rq to
 scsi_prep_state_check()

On Sat, 2017-10-14 at 02:05 +0800, Ming Lei wrote:
> In the following patch, we will implement scsi_get_budget()
> which need to call scsi_prep_state_check() when rq isn't
> dequeued yet.

My understanding is that this change is only needed because scsi_mq_get_budget()
calls scsi_prep_state_check() with the req argument set to NULL. Since
scsi_prep_state_check() tests for sdev states other than SDEV_RUNNING and since
the purpose of this series is to optimize performance for the case SDEV_RUNNING
I'm not sure it's a good idea to make scsi_mq_get_budget() call
scsi_prep_state_check(). And if scsi_mq_get_budget() wouldn't call
scsi_prep_state_check() then this patch is not necessary.

Bart.