linux-kernel - Re: [PATCH v4 1/1] nvme: multipath: Implemented new iopolicy "queue-depth"

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Date: Thu, 23 May 2024 08:23:34 +0200
From: Hannes Reinecke <hare@...e.de>
To: John Meneghini <jmeneghi@...hat.com>, kbusch@...nel.org, hch@....de,
 sagi@...mberg.me, emilne@...hat.com
Cc: linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
 jrani@...estorage.com, randyj@...estorage.com, hare@...nel.org
Subject: Re: [PATCH v4 1/1] nvme: multipath: Implemented new iopolicy
 "queue-depth"

On 5/22/24 17:42, John Meneghini wrote:
> From: "Ewan D. Milne" <emilne@...hat.com>
> 
> The round-robin path selector is inefficient in cases where there is a
> difference in latency between paths.  In the presence of one or more
> high latency paths the round-robin selector continues to use the high
> latency path equally. This results in a bias towards the highest latency
> path and can cause a significant decrease in overall performance as IOs
> pile on the highest latency path. This problem is acute with NVMe-oF
> controllers.
> 
> The queue-depth policy instead sends I/O requests down the path with the
> least amount of requests in its request queue. Paths with lower latency
> will clear requests more quickly and have less requests in their queues
> compared to higher latency paths. The goal of this path selector is to
> make more use of lower latency paths which will bring down overall IO
> latency and increase throughput and performance.
> 
> Signed-off-by: Thomas Song <tsong@...estorage.com>
> [emilne: patch developed by Thomas Song @ Pure Storage, fixed whitespace
>        and compilation warnings, updated MODULE_PARM description, and
>        fixed potential issue with ->current_path[] being used]
> Signed-off-by: Ewan D. Milne <emilne@...hat.com>
> [jmeneghi: vairious changes and improvements, addressed review comments]
> Signed-off-by: John Meneghini <jmeneghi@...hat.com>
> Link: https://lore.kernel.org/linux-nvme/20240509202929.831680-1-jmeneghi@redhat.com/
> Tested-by: Marco Patalano <mpatalan@...hat.com>
> Reviewed-by: Randy Jennings <randyj@...estorage.com>
> Tested-by: Jyoti Rani <jrani@...estorage.com>
> ---
>   drivers/nvme/host/core.c      |  2 +-
>   drivers/nvme/host/multipath.c | 91 +++++++++++++++++++++++++++++++++--
>   drivers/nvme/host/nvme.h      |  8 +++
>   3 files changed, 96 insertions(+), 5 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@...e.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich