linux-kernel - Re: [PATCH 1/5] scsi: hisi_sas: Add host_tagset

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Message-ID: <c60bb344-5ac1-4e6a-b68c-217c403f7017@oracle.com>
Date: Mon, 31 Mar 2025 08:43:47 +0100
From: John Garry <john.g.garry@...cle.com>
To: yangxingui <yangxingui@...wei.com>, Yihang Li <liyihang9@...wei.com>,
        martin.petersen@...cle.com, James.Bottomley@...senPartnership.com
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, liuyonglong@...wei.com, prime.zeng@...ilicon.com,
        linux-ide@...r.kernel.org
Subject: Re: [PATCH 1/5] scsi: hisi_sas: Add host_tagset_enable module param
 for v3 hw

On 29/03/2025 09:49, yangxingui wrote:
> Hi，John
> 
> On 2025/3/29 16:50, John Garry wrote:
>> On 29/03/2025 07:32, Yihang Li wrote:
>>
>> +
>>
>>> From: Xingui Yang<yangxingui@...wei.com>
>>>
>>> After driver exposes all HW queues and application submits IO to 
>>> multiple
>>> queues in parallel, if NCQ and non-NCQ commands are mixed to sata disk,
>>> ata_qc_defer() causes non-NCQ commands to be requeued and possibly 
>>> repeated
>>> forever.
>>
>> I don't think that it is a good idea to mask out bugs with module 
>> parameters.
>>
>> Was this the same libata/libsas issue reported some time ago?
> 
> Yeah，related to this issue: https://lore.kernel.org/linux-block/ 
> eef1e927-c9b2-c61d-7f48-92e65d8b0418@...wei.com/
> 
> And, Niklas tried to help fix this problem: https://lore.kernel.org/ 
> linux-scsi/ZynmfyDA9R-lrW71@...en/
> 
> Considering that there is no formal solution yet. And our users rarely 
> use SATA disks and SAS disks together on a single machine. For this 
> reason, they can flexibly turn off the exposure of multiple queues in 
> the scenario of using only SATA disks. In addition, it is also 
> convenient to conduct performance comparison tests to expose multiple 
> hardware queues and single queues.
> 

The change in this series does not even solve the issues, as:
- you do not guarantee no SAS/SATA mix without that module param enabled
- the driver still uses managed interrupts in both cases, so with 
disabling host_tagset you are now exposed to CPU hotplug issue of IO 
being in-flight when HW queue interrupt is shutdown

And pm8001 driver will have the same issue, so we need to find a proper fix.

Let me consider this issue more.