RE: [PATCH] scsi: scsi_host_queue_ready: increase busy count early

From: <Don.Brace@microchip.com>
To: <pmenzel@molgen.mpg.de>, <john.garry@huawei.com>, <mwilck@suse.com>
Cc: <jejb@linux.vnet.ibm.com>, <linux-scsi@vger.kernel.org>,
	<hare@suse.de>, <Kevin.Barnett@microchip.com>, <hare@suse.com>,
	<ming.lei@redhat.com>, <martin.petersen@oracle.com>,
	<buczek@molgen.mpg.de>, <it+linux-scsi@molgen.mpg.de>
Subject: RE: [PATCH] scsi: scsi_host_queue_ready: increase busy count early
Date: Wed, 3 Feb 2021 15:30:07 +0000	[thread overview]
Message-ID: <SN6PR11MB284853B4E54C9F3626C0F17BE1B49@SN6PR11MB2848.namprd11.prod.outlook.com> (raw)
In-Reply-To: <e60ed23d-676f-a1f9-81a1-44d2ca97f9da@molgen.mpg.de>

-----Original Message-----
From: Paul Menzel [mailto:pmenzel@molgen.mpg.de] 
Subject: Re: [PATCH] scsi: scsi_host_queue_ready: increase busy count early

>>> Confirmed my suspicions - it looks like the host is sent more 
>>> commands than it can handle. We would need many disks to see this 
>>> issue though, which you have.
>>>
>>> So for stable kernels, 6eb045e092ef is not in 5.4 . Next is 5.10, 
>>> and I suppose it could be simply fixed by setting .host_tagset in 
>>> scsi host template there.
>>>
>>> Thanks,
>>> John
>>> --
>>> Don: Even though this works for current kernels, what would chances 
>>> of this getting back-ported to 5.9 or even further?
>>>
>>> Otherwise the original patch smartpqi_fix_host_qdepth_limit would 
>>> correct this issue for older kernels.
>>
>> True. However this is 5.12 material, so we shouldn't be bothered by 
>> that here. For 5.5 up to 5.9, you need a workaround. But I'm unsure 
>> whether smartpqi_fix_host_qdepth_limit would be the solution.
>> You could simply divide can_queue by nr_hw_queues, as suggested 
>> before, or even simpler, set nr_hw_queues = 1.
>>
>> How much performance would that cost you?
>>
>> Distribution kernels would be yet another issue, distros can backport 
>> host_tagset and get rid of the issue.
>
> Aren't they (distros) the only issue? As I mentioned above, for 5.10 
> mainline stable, I think it's reasonable to backport a patch to set 
> .host_tagset for the driver.

Indeed. As per the Linux kernel Web site [1]: 5.5 and 5.9 are not maintained anymore (EOL) upstream. So, if distributions decided to go with another Linux kernel release, it’s their job to backport things. If the commit message is well written, and contains the Fixes tag, their tooling should be able to pick it up.

Kind regards,

Paul

[1]: https://www.kernel.org/

I remove patch smartpqi-fix_host_qdepth_limit and replaced it with a patch that sets host_tagset = 1 in function pqi_register_scsi

Thanks to all for  your hard work.
Don