linux-kernel - Re: [PATCH v1 5/9] block: loop: convert to blk-mq

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Date:	Wed, 27 Aug 2014 12:29:55 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Maxim Patlasov <mpatlasov@...allels.com>
Cc:	Ming Lei <ming.lei@...onical.com>, Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Zach Brown <zab@...bo.net>,
	Kent Overstreet <kmo@...erainc.com>, open list:
	AIO <linux-aio@...ck.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>, ;
Subject: Re: [PATCH v1 5/9] block: loop: convert to blk-mq

On Wed, Aug 27, 2014 at 08:08:59PM +0400, Maxim Patlasov wrote:
...
> 1) /dev/loop0 of 3.17.0-rc1 with Ming's patches applied -- 11K iops
> 2) the same as above, but call loop_queue_work() directly from 
> loop_queue_rq() -- 270K iops
> 3) /dev/nullb0 of 3.17.0-rc1 -- 380K iops
> 
> Taking into account so big difference (11K vs. 270K), would it be worthy 
> to implement pure non-blocking version of aio_kernel_submit() returning 
> error if blocking needed? Then loop driver (or any other in-kernel user) 
> might firstly try that non-blocking submit as fast-path, and, only if 
> it's failed, fall back to queueing.

What filesystem is the backing file for loop0 on?  O_DIRECT access as 
Ming's patches use should be non-blocking, and if not, that's something 
to fix.

		-ben
-- 
"Thought is the essence of where you are now."
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