Re: [PATCH RFC] nvme-multipath: optimize path selection in queue-depth policy

[Keith Busch <kbusch@kernel.org>]

On Wed, May 07, 2026 at 04:15:41PM +0200, Xose Vazquez Perez wrote:
> Move the zero-depth check inside the optimized path case to enable early
> exit. It avoids redundant condition checks for non-optimized paths, and
> eliminates the per-iteration check at the end of the loop, improving the
> performance.

The existing code is already well optimized, and even gcc figures out
that the min_depth_opt is only updated in the case as it is.
 
> Cc: Aviv Coro <aviv.coro@ibm.com>
> Cc: Bart Van Assche <bvanassche@acm.org>
> Cc: Benjamin Marzinski <bmarzins@redhat.com>
> Cc: Brian Bunker <brian@purestorage.com>
> Cc: Caleb Sander <csander@purestorage.com>
> Cc: Chaitanya Kulkarni <kch@nvidia.com>
> Cc: Chris Leech <cleech@redhat.com>
> Cc: Christophe Varoqui <christophe.varoqui@opensvc.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Clayton Skaggs <claytons@netapp.com>
> Cc: Constantine Gavrilov <cgavrilov@infinidat.com>
> Cc: Daniel Wagner <wagi@kernel.org>
> Cc: David Santamaría Rogado <howl.nsp@gmail.com>
> Cc: Dmitry V. Levin <ldv@strace.io>
> Cc: Ewan D. Milne <emilne@redhat.com>
> Cc: Ewan Milne <emilne@redhat.com>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: James Smart <jsmart2021@gmail.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: John Meneghini <jmeneghi@redhat.com>
> Cc: Jyoti Rani <jrani@purestorage.com>
> Cc: Keith Busch <kbusch@kernel.org>
> Cc: Li Xiaokeng <lixiaokeng@huawei.com>
> Cc: Marco Patalano <mpatalan@redhat.com>
> Cc: Martin Belanger <martin.belanger@dell.com>
> Cc: Martin George <Martin.George@netapp.com>
> Cc: Martin Wilck <mwilck@suse.com>
> Cc: Matthias Rudolph <Matthias.Rudolph@hitachivantara.com>
> Cc: Maurizio Lombardi <mlombard@arkamax.eu>
> Cc: NetApp RDAC team <ng-eseries-upstream-maintainers@netapp.com>
> Cc: Nilay Shroff <nilay@linux.ibm.com>
> Cc: Randy Jennings <randyj@purestorage.com>
> Cc: Sagi Grimberg <sagi@grimberg.me>
> Cc: Simon Schricker <sschricker@suse.de>
> Cc: Steven Schremmer <Steve.Schremmer@netapp.com>
> Cc: Thomas Song <tsong@purestorage.com>
> Cc: Uday Shankar <ushankar@purestorage.com>
> Cc: Vasuki Manikarnike <vasuki.manikarnike@hpe.com>
> Cc: Wayne Berthiaume <Wayne.Berthiaume@dell.com>
> Cc: Zou Ming <zouming.zouming@huawei.com>
> Cc: BLOCK-ML <linux-block@vger.kernel.org>
> Cc: DM_DEVEL-ML <dm-devel@lists.linux.dev>
> Cc: NVME-ML <linux-nvme@lists.infradead.org>
> Cc: SCSI-ML <linux-scsi@vger.kernel.org>

This is quite an eggregious CC list...

> Status: Compile-tested only. UNTESTED on real hardware.
> 
> [I do not have access to this kind of hardware]

What compelled you to propose this change, then?