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Date: Mon, 14 Apr 2025 08:09:59 +0200
From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Nilay Shroff <nilay@linux.ibm.com>,
	Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>,
	Thomas =?iso-8859-1?Q?Hellstr=F6m?= <thomas.hellstrom@linux.intel.com>
Subject: Re: [PATCH 05/15] block: simplify elevator reset for updating
 nr_hw_queues
Message-ID: <20250414060959.GB6451@lst.de>
References: <20250410133029.2487054-1-ming.lei@redhat.com> <20250410133029.2487054-6-ming.lei@redhat.com> <20250410153417.GA12430@lst.de> <Z_xdtNiZb38ubXVe@fedora>
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In-Reply-To: <Z_xdtNiZb38ubXVe@fedora>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Apr 14, 2025 at 08:58:28AM +0800, Ming Lei wrote:
> > Coming back to this after looking through the next patches.
> > 
> > Why do we even need the __elevator_change call here?  We've not
> > actually disabled the elevator, and we prevent other callers
> > from changing it.
> > 
> > As you pass in the force argument this now always calls
> > elevator_switch and thus blk_mq_init_sched.  But why?
> 
> sched tags is built over hctx and depends on ->nr_hw_queues,
> when nr_hw_queues is changed, sched tags has to be rebuilt.

Can you add a comment explaining this?