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From: John Garry <>
To: Ming Lei <>
Cc: <>, <>,
	<>, <>,
	<>, <>,
	chenxiang <>
Subject: Re: [PATCH 6/6] scsi: hisi_sas: Expose multiple hw queues for v3 as experimental
Date: Tue, 12 Nov 2019 13:54:44 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20191112111053.GA31697@ming.t460p>

>> I mentioned in the thread "blk-mq: improvement on handling IO during CPU
>> hotplug" that I was using this series to test that patchset.
>> So just with this patchset (and without yours), I get what looks like some
>> IO errors in the LLDD. The error is an underflow error. I can't figure out
>> what is the cause.

Hi Ming,

> Can you post the error log? Or interpret the 'underflow error' from hisi
> sas or scsi viewpoint?

The check here fails:

Indeed, no data is received.

>> I'm wondering if the SCSI command is getting corrupted someway.
> Why do you think the command is corrupted?

I considered that the underflow may occur if we were to clobber a SCSI 
command/request from another hctx and zero some fields, which is 
detected as an underflow. But that's just guessing.

However do I find if I set shost->can_queue = HISI_SAS_MAX_COMMANDS / 
#queues, then no issue. But maybe that's a coincidence. For this, total 
queue depth = HISI_SAS_MAX_COMMANDS. I don't see the impact of that.

I need to test that more.

>>>> +	if (expose_mq_experimental) {
>>>> +		shost->can_queue = HISI_SAS_MAX_COMMANDS;
>>>> +		shost->cmd_per_lun = HISI_SAS_MAX_COMMANDS;
>>> The above is contradictory with current 'nr_hw_queues''s meaning,
>>> see commit on Scsi_Host.nr_hw_queues.
>> Right, so I am generating the hostwide tag in the LLDD. And the Scsi
>> host-wide host_busy counter should ensure that we don't pump too much IO to
>> the HBA.
> Even without the host-wide host_busy, your approach should work if you
> build the hisi sas tag correctly(uniquely), just not efficiently.

Yes, I do that.

> suggest you to collect trace and observe if request with expected hisi sas
> tag is sent to hardware.

I can add some debug for that. What trace do you mean?

> BTW, the patch of 'scsi: core: avoid host-wide host_busy counter for scsi_mq'
> will be merged to v5.5 if everything is fine.

Yeah, it seems a good change.


  reply	other threads:[~2019-11-12 13:54 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-24 14:21 [PATCH 0/6] hisi_sas: Expose multiple hw queues for v3 hw as experimental John Garry
2019-10-24 14:21 ` [PATCH 1/6] scsi: hisi_sas: Use sbitmap for IPTT management John Garry
2019-10-24 14:21 ` [PATCH 2/6] scsi: hisi_sas: Pass scsi_cmnd pointer to hisi_sas_hw.slot_index_alloc John Garry
2019-10-24 14:21 ` [PATCH 3/6] scsi: hisi_sas: Add bitmaps_alloc_v3_hw() John Garry
2019-10-24 14:21 ` [PATCH 4/6] scsi: hisi_sas: Add slot_index_alloc_v3_hw() and slot_index_free_v3_hw() John Garry
2019-10-24 14:21 ` [PATCH 5/6] scsi: hisi_sas: Split interrupt_init_v3_hw() John Garry
2019-10-24 14:21 ` [PATCH 6/6] scsi: hisi_sas: Expose multiple hw queues for v3 as experimental John Garry
2019-10-27  8:19   ` Ming Lei
2019-11-11 14:02     ` John Garry
2019-11-12 11:10       ` Ming Lei
2019-11-12 13:54         ` John Garry [this message]
2019-11-12 14:35           ` John Garry
2019-10-25 16:04 ` [PATCH 0/6] hisi_sas: Expose multiple hw queues for v3 hw " John Garry

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