linux-kernel - Re: [PATCH 0/2] Introduce the request handling for dm-crypt

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Date:	Fri, 13 Nov 2015 10:05:15 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Baolin Wang <baolin.wang@...aro.org>
Cc:	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>,
	axboe@...nel.dk, Alasdair G Kergon <agk@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
	neilb@...e.com, tj@...nel.org, jmoyer@...hat.com,
	keith.busch@...el.com, bart.vanassche@...disk.com,
	linux-raid@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	"Garg, Dinesh" <dineshg@...cinc.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Introduce the request handling for dm-crypt

On Friday 13 November 2015 10:05:28 Baolin Wang wrote:
> 
> Well, I did a simple test with dd reading, cause my engine limitation is 1M,
> (1) so the time like below when handle 1M at one time.
> 1048576 bytes (1.0 MB) copied, 0.0841235 s, 12.5 MB/s
> 1048576 bytes (1.0 MB) copied, 0.0836294 s, 12.5 MB/s
> 1048576 bytes (1.0 MB) copied, 0.0836526 s, 12.5 MB/s
> 
> (2) These handle 64K at one time * 16 times
> 1048576 bytes (1.0 MB) copied, 0.0937223 s, 11.2 MB/s
> 1048576 bytes (1.0 MB) copied, 0.097205 s, 10.8 MB/s
> 1048576 bytes (1.0 MB) copied, 0.0935884 s, 11.2 MB/s
> 
> Here is a 10ms level difference, try to image if the hardware engine's
> throughput is bigger than that. But like Jens said, we can measure it
> by the performance data.

The absolute numbers look really low. Does this include writing to
a hard drive? That would certainly make the difference appear
less significant.

Could you try backing this with a ram disk backing for comparison,
and also use 'time dd' to show the CPU utilization for all cases?
For completeness, including cpu-only performance might also help
put this into perspective.

	Arnd
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