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From: Arnd Bergmann <arnd@arndb.de>
To: Manoj Iyer <manoj.iyer@canonical.com>
Subject: Re: [PATCH] mmc: Added quirks for Ricoh 1180:e823 lower base clock frequency
Date: Wed, 13 Jul 2011 18:35:25 +0200
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On Wednesday 13 July 2011, Manoj Iyer wrote:
> 
> Chris/Arnd,
> 
> Here is a series of test I did with the patched kernel.

> == cold boot insert SD card ==
> u@u:~/flash/flashbench$ sudo ./flashbench -O --erasesize=$[4 * 1024 * 
> 1024] --blocksize=$[256 * 1024] /dev/mmcblk0  --open-au-nr=2
> 4MiB    4.96M/s
> 2MiB    6.3M/s
> 1MiB    6.23M/s
> 512KiB  6.23M/s
> 256KiB  6.26M/s

The very first one obviously triggers a garbage collection.
Everything after that is well within measuring accuracy around 6.25MB/s

> On Wed, 13 Jul 2011, Chris Ball wrote:

> >
> > That makes sense.  Do you think this explains Manoj getting a slower
> > first file copy speed (757ms vs. 480ms) after applying his patch?
> > (Manoj, perhaps you could retry your test without GC being needed?)

Yes. For a single sample, it can easily explain differences up to 500ms.
You have to average out file system benchmarks across a lot of files
to be sure.

> > What would we expect lowering the SD base clock frequency from 200MHz
> > to 50MHz to do to performance theoretically?

Not much. This card only has a 6MB/s write speed, which is well below
what a 50 MHz bus can do. It mgiht be different on a fast eMMC device
or a Sandisk Extreme Pro UHS-1 card.

	Arnd