linux-kernel - Re: [PATCH v7] NVMe: conversion to blk-mq

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Date:	Fri, 13 Jun 2014 15:28:58 -0600
From:	Jens Axboe <axboe@...com>
To:	Keith Busch <keith.busch@...el.com>
CC:	Matias Bjørling <m@...rling.me>,
	Matthew Wilcox <willy@...ux.intel.com>,
	"sbradshaw@...ron.com" <sbradshaw@...ron.com>,
	"tom.leiming@...il.com" <tom.leiming@...il.com>,
	"hch@...radead.org" <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Subject: Re: [PATCH v7] NVMe: conversion to blk-mq

On 06/13/2014 01:22 PM, Keith Busch wrote:
> One performance oddity we observe is that servicing the interrupt on the
> thread sibling of the core that submitted the I/O is the worst performing
> cpu you can chose; it's actually better to use a different core on the
> same node. At least that's true as long as you're not utilizing the cpus
> for other work, so YMMV.

This doesn't match what I see here. Just ran some test cases - both
sync, and higher QD. For sync performance, core or thread sibling is the
best choice, other CPUs next. That is pretty logical.

For a more loaded run, thread sibling ends up being a better choice than
core, since core runs out of steam (255K vs 275K here). And thread
sibling is still a marginally better choice than some other core on the
same node.

Which pretty much matches my expectations of what the best mappings
would be.

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