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Date: Thu, 28 May 2026 10:44:28 +0200
From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, guzebing <guzebing1612@gmail.com>,
	axboe@kernel.dk, sagi@grimberg.me, linux-nvme@lists.infradead.org,
	linux-kernel@vger.kernel.org, Guzebing <guzebing@bytedance.com>
Subject: Re: [RFC PATCH 0/1] nvme-pci: detect I/O queue depth changes after
 reset
Message-ID: <20260528084428.GA8248@lst.de>
References: <20260527075320.3178600-1-guzebing1612@gmail.com> <20260527131951.GA11071@lst.de> <ahewZiV3n6qG1Jhm@kbusch-mbp>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Wed, May 27, 2026 at 09:03:02PM -0600, Keith Busch wrote:
> On Wed, May 27, 2026 at 03:19:51PM +0200, Christoph Hellwig wrote:
> > On Wed, May 27, 2026 at 03:53:19PM +0800, guzebing wrote:
> > > This RFC instead takes the smaller approach of detecting the reset-time
> > > CAP.MQES change and making it visible.  If the live I/O queue depth
> > > shrinks, reset recovery is failed before recreating I/O queues.  If it
> > > grows, the driver warns and continues with the existing queue resources.
> > 
> > Unlike the other version this at least sounds doable without creating
> > a complete mess.  So if we can live with this version that'd make me
> > much happier.
> 
> Abandoning the device here sounds pretty harsh when blk-mq already
> supports user space decreasing the q-depth on a live queue. Why can't
> the driver do the same thing?

Reducing capabilities with a firmware upgrade is a losing proposition,
there's just way too many things that can go wrong.

And reducing the queue depth is one of the haіriest operation in
blk-mq.  I wish we had never supported it, but allowing it with a
remove trigger sounds really bad.