linux-kernel - Re: [PATCH v8 2/2] nvme-multipath: implement "queue-depth" iopolicy

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Date: Wed, 26 Jun 2024 08:19:46 +0000
From: Chaitanya Kulkarni <chaitanyak@...dia.com>
To: John Meneghini <jmeneghi@...hat.com>, "kbusch@...nel.org"
	<kbusch@...nel.org>, "hch@....de" <hch@....de>, "sagi@...mberg.me"
	<sagi@...mberg.me>
CC: "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"emilne@...hat.com" <emilne@...hat.com>, "jrani@...estorage.com"
	<jrani@...estorage.com>, "randyj@...estorage.com" <randyj@...estorage.com>,
	"hare@...nel.org" <hare@...nel.org>
Subject: Re: [PATCH v8 2/2] nvme-multipath: implement "queue-depth" iopolicy

On 6/25/24 05:26, John Meneghini wrote:
> From: Thomas Song<tsong@...estorage.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 path selector sends I/O down the path with the lowest
> number of requests in its request queue. Paths with lower latency will
> clear requests more quickly and have less requests queued 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]
> Co-developed-by: Ewan D. Milne<emilne@...hat.com>
> Signed-off-by: Ewan D. Milne<emilne@...hat.com>
> [jmeneghi: various changes and improvements, addressed review comments]
> Co-developed-by: John Meneghini<jmeneghi@...hat.com>
> 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>
> Tested-by: John Meneghini<jmeneghi@...hat.com>
> Reviewed-by: Hannes Reinecke<hare@...e.de>

thanks for sharing github link, those scripts are in-general helpful ...

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>

-ck