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Date: Wed, 22 May 2024 09:12:29 -0400
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Subject: Re: [PATCH v3 1/1] nvme: multipath: Implemented new iopolicy
 "queue-depth"
To: Nilay Shroff <nilay@linux.ibm.com>, Sagi Grimberg <sagi@grimberg.me>,
 kbusch@kernel.org, hch@lst.de, emilne@redhat.com
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From: John Meneghini <jmeneghi@redhat.com>
Organization: RHEL Core Storge Team
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On 5/22/24 06:48, Nilay Shroff wrote:
>> 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
>>
>>
> I think with Keith's recent proposed patch for fixing io accounting on failover, the
> nvme_mpath_end_request() would be called even for cancelled IO and so the nr_active
> counter shall be adjusted correctly for cancelled IO requests. Having said that, IMO
> you shall consider moving initialization of nr_active counter to nvme_mpath_init_identify()
> as that's common function invoked from regular controller initialization code path as well
> the reset code path.

Agreed. I'll do that in V4 of the patch set.

/John