linux-kernel - Re: [PATCH V7 4/6] blk-mq: introduce .get_budget and .put_budget in blk_mq

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Message-ID: <1508169991.2493.17.camel@wdc.com>
Date:   Mon, 16 Oct 2017 16:06:32 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "hare@...e.de" <hare@...e.de>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "himanshu.madhani@...ium.com" <himanshu.madhani@...ium.com>,
        "tom81094@...il.com" <tom81094@...il.com>,
        "paolo.valente@...aro.org" <paolo.valente@...aro.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "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>,
        "james.smart@...adcom.com" <james.smart@...adcom.com>
Subject: Re: [PATCH V7 4/6] blk-mq: introduce .get_budget and .put_budget in
 blk_mq_ops

On Mon, 2017-10-16 at 13:30 +0200, Hannes Reinecke wrote:
> On Fri, Oct 13, 2017 at 05:08:52PM +0000, Bart Van Assche wrote:
> > (+Himanshu Madhani)
> > 
> > Himanshu, do you perhaps know whether it is safe to increase cmd_per_lun for
> > the qla2xxx initiator driver to the scsi_host->can_queue value?
> 
> '3' is just a starting point; later on it'll be adjusted via scsi_change_depth().
> Looks like it's not working correctly with blk-mq, though.

Hello Hannes,

Isn't the purpose of scsi_change_queue_depth() to change the sdev queue_depth
only? As far as I know there is only one assignment of shost->cmd_per_lun in
the SCSI core and that's the following assignment in scsi_host_alloc():

	shost->cmd_per_lun = sht->cmd_per_lun;

Bart.