Re: [PATCH] mmc: Added quirks for Ricoh 1180:e823 lower base clock frequency

[Manoj Iyer <manoj.iyer@canonical.com>]

Chris,

Do you think that lowering the controller speed to 50Mhz in case we have a 
failure is a better idea than reducing the speed for all e823 ricoh 
controllers? I can send a V2 of the patch. What do you think ?

On Wed, 13 Jul 2011, Arnd Bergmann wrote:

> 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
>
>

--
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Manoj Iyer
Ubuntu/Canonical
Hardware Enablement
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