linux-kernel - Re: [PATCH 0/2] nvme-pic: improve max I/O queue handling

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Message-ID: <20201112145325.GC2573679@dhcp-10-100-145-180.wdc.com>
Date:   Thu, 12 Nov 2020 06:53:25 -0800
From:   Keith Busch <kbusch@...nel.org>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH 0/2] nvme-pic: improve max I/O queue handling

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@...nel.org>