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Date:   Fri, 30 Sep 2022 11:20:46 +0100
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Subject: Re: [PATCH v2 4/6] scsi: pm8001: Use sas_task_find_rq() for tagging
To:     Jinpu Wang <jinpu.wang@ionos.com>, <damien.lemoal@wdc.com>
CC:     <jejb@linux.ibm.com>, <martin.petersen@oracle.com>, <hare@suse.de>,
        <linux-scsi@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linuxarm@huawei.com>, <ipylypiv@google.com>,
        <changyuanl@google.com>, <hch@lst.de>, <yanaijie@huawei.com>
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From:   John Garry <john.garry@huawei.com>
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On 30/09/2022 10:17, Jinpu Wang wrote:
> On Fri, Sep 30, 2022 at 11:03 AM John Garry<john.garry@huawei.com>  wrote:
>> The request associated with a scsi command coming from the block layer
>> has a unique tag, so use that when possible for getting a CCB.
>>
>> Unfortunately we don't support reserved commands in the SCSI midlayer yet,
>> so in the interim continue to manage those tags internally (along with
>> tags for private commands).
>>
>> Signed-off-by: John Garry<john.garry@huawei.com>
> Reviewed-by: Jack Wang<jinpu.wang@ionos.com>
> nice, I would expect this can improve performance, do you have numbers?

Unfortunately my system hangs after I run for an appreciable period of 
time. I normally get around it by turning on much heavy debug options, 
but that would not be much use for performance testing.

But we did get considerable performance improvement for hisi_sas when we 
made the equivalent change.

Damien, if you are interested then sharing any results would be great.

BTW, I do notice that we still have this global lock in delivery path 
which should be removed at some stage:

int mvs_queue_command(struct sas_task *task, gfp_t gfp_flags)
{
	...

	spin_lock_irqsave(&mvi->lock, flags);
	rc = mvs_task_prep(task, mvi, is_tmf, tmf, &pass);
	...
	spin_unlock_irqrestore(&mvi->lock, flags);
}

That really will affect performance...

Thanks,
John