linux-kernel - Re: [PATCH v3 1/1] nvme: multipath: Implemented new iopolicy "queue-depth"

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Message-ID: <8f5ad047-be0b-471c-a708-f2bc464d29ef@redhat.com>
Date: Tue, 21 May 2024 10:44:07 -0400
From: John Meneghini <jmeneghi@...hat.com>
To: Sagi Grimberg <sagi@...mberg.me>, Nilay Shroff <nilay@...ux.ibm.com>,
 kbusch@...nel.org, hch@....de, emilne@...hat.com
Cc: linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
 jrani@...estorage.com, randyj@...estorage.com, hare@...nel.org
Subject: Re: [PATCH v3 1/1] nvme: multipath: Implemented new iopolicy
 "queue-depth"

On 5/21/24 06:16, Sagi Grimberg wrote:
>>>
>>> Exactly, nvme_mpath_init_ctrl resets the counter.
>>
>> Except you're right, the counter reset needs to move to nvme_mpath_init_identify()
>> or some place that is called on every controller reset.
> 
> This however raises the question of how much failover/reset tests this patch has seen...

I has received quite a bit of testing with failover and controller resets.  I shared some of the testing that was done at LSFMM 
last week.

It has received enough testing to make me confident that this code is safe.  That is: it won't panic, corrupt data, or otherwise 
do any harm.  We believe the error paths will not be affected by this change... but I agree that running the error paths could 
negatively impact the accuracy of the nr_active counters... which could lead to an inaccurate outcome with the queue-depth policy.

I agree the nr_counter initialize should move to nvme_mpath_init_identify(), or maybe be done there in addition to in 
nvme_mpath_init_ctrl(). I'm will to make that change now... if that's what people want.  I don't think it would require any 
extensive retesting.

/John