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

[John Garry <john.garry@huawei.com>]

On 02/02/2021 20:48, Martin Wilck wrote:
> On Tue, 2021-02-02 at 20:04 +0000, Don.Brace@microchip.com wrote:
>> -----Original Message-----
>> From: John Garry [mailto:john.garry@huawei.com]
>> 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.

Thanks,
John