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Subject: Re: [PATCH 0/2] nvme-pic: improve max I/O queue handling
To:     Keith Busch <kbusch@kernel.org>
Cc:     linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
        Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>
References: <20201112082302.82441-1-schnelle@linux.ibm.com>
 <20201112145325.GC2573679@dhcp-10-100-145-180.wdc.com>
From:   Niklas Schnelle <schnelle@linux.ibm.com>
Message-ID: <10908f20-7e18-e967-76dd-1a38e216b378@linux.ibm.com>
Date:   Thu, 12 Nov 2020 16:45:35 +0100
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On 11/12/20 3:53 PM, Keith Busch wrote:
> On Thu, Nov 12, 2020 at 09:23:00AM +0100, Niklas Schnelle wrote:
>> while searching for a bug around zPCI + NVMe IRQ handling on a distro
>> kernel, I got confused around handling of the maximum number
>> of I/O queues in the NVMe driver.
>> I think I groked it in the end but would like to propose the following
>> improvements, that said I'm quite new to this code.
>> I tested both patches on s390x (with a debug config) and x86_64 so
>> with both data center and consumer NVMes.
>> For the second patch, since I don't own a device with the quirk, I tried
>> always returning 1 from nvme_max_io_queues() and confirmed that on my
>> Evo 970 Pro this resulted in about half the performance in a fio test
>> but did not otherwise break things. I couldn't find a reason why
>> allocating only the I/O queues we actually use would be problematic in
>> the code either but I might have missed something of course.
> 
> I don't think you missed anything, and the series looks like a
> reasonable cleanup. I suspect the code was left over from a time when we
> didn't allocate the possible queues up-front.
> 
> Reviewed-by: Keith Busch <kbusch@kernel.org>
> 

You got to get something wrong, I hope in this case it's just the subject
of the cover letter :D
Thanks for the review, I appreciate it. Might be getting ahead of
myself but I'm curious who would take this change through their
tree if accepted?