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