linux-kernel - Re: [PATCH RFC 0/2] Convert from bio-based to blk-mq

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Message-ID: <52540674.5030402@bjorling.me>
Date:	Tue, 08 Oct 2013 15:19:48 +0200
From:	Matias Bjørling <m@...rling.me>
To:	Matthew Wilcox <willy@...ux.intel.com>
CC:	axboe@...nel.dk, linux-kernel@...r.kernel.org,
	linux-nvme@...ts.infradead.org
Subject: Re: [PATCH RFC 0/2] Convert from bio-based to blk-mq

On 10/08/2013 03:10 PM, Matthew Wilcox wrote:
> On Tue, Oct 08, 2013 at 11:34:20AM +0200, Matias Bjørling wrote:
>> The nvme driver implements itself as a bio-based driver. This primarily because
>> of high lock congestion for high-performance nvm devices. To remove the
>> congestion, a multi-queue block layer is being implemented.
>
> Um, no.  You'll crater performance by adding another memory allocation
> (of the struct request).  multi-queue is not the solution.
>

Agree that there shouldn't be yet another allocation. blk-mq allocates 
the requests upfront for that reason. Additionally, nvme_cmd_info can be 
handled within the request payload.
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