linux-kernel - Re: [PATCH 1/3] blk-mq: add an API to estimate hardware queue node

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Message-ID: <20160329164722.GA1208161@devbig084.prn1.facebook.com>
Date:	Tue, 29 Mar 2016 09:47:23 -0700
From:	Shaohua Li <shli@...com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	<linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<axboe@...com>, <Kernel-team@...com>
Subject: Re: [PATCH 1/3] blk-mq: add an API to estimate hardware queue node

On Tue, Mar 29, 2016 at 12:24:43AM -0700, Christoph Hellwig wrote:
> On Fri, Mar 25, 2016 at 02:36:30PM -0700, Shaohua Li wrote:
> > we allocate most data structure in device's node, but some data
> > structures are not for DMA and mostly used by specific cpus/node which
> > could diff from device's node. Allocating such hot data in device's
> > node doesn't make sense. Add an API to estimate hardware queue node.
> > This can be used before blk-mq actually establishes the mapping. This
> > API runs slow, but it only used in initialization time.
> 
> I think this is the wrong way around.  I've got some proprotype code
> that just leaves the cpu assignments to the drivers and picks it up
> in blk-mq.  Give me a few days to post it..

This looks weird, shouldn't the cpu assignment be determined by block
core (blk-mq) because block core decides how to use the queue?