Re: eMMC low write speed

[Praveen G K]

On Fri, Sep 23, 2011 at 7:11 AM, Timo Kokkonen <kaapeli@xxxxxxxxxxxx> wrote:
> On 09/23/11 06:03, Praveen G K wrote:
>> Hi Qiang,
>>
>>
>> On Thu, Sep 22, 2011 at 7:16 PM, Qiang LIU <godliuqiang@xxxxxxxxx> wrote:
>>> Hi,
>>>
>>> I suggest you change another eMMC card or try SDHC card. It seems like
>>> a card issue.
>>
>> Thanks for the response.  So, do you think this has nothing to do with
>> the caching or any such issues, since it is only every 63rd and 64th
>> transfer causing this issue?
>
> It is very much possible that the card itself does something internally
> on every 63rd or 64th transfer. Such as wear leveling management on the
> nand or perhaps some copy-on-write operations if the transfers are not
> taking place in contiguous blocks.

The way I am testing it is as follows
time -p dd if=/dev/zero of=/dev/mmcblk0 bs=512k count=10 (I have tried
different values for count)

When I especially try for count = 10, I see the request completed in
0.25 seconds or as high as 1 second.  When it is 0.25 s, the speed is
20MBps, and when it is 1s, the speed is 5MBps.  So, I am not sure
whether I am missing something here.
I am using the Sandisk SDIN5C1-4G card for testing.  Any other card of
the same family, I see only a speed of 5MBps.

> As suggested above, you could try with another eMMC or SDCH card if it
> makes a different (if possible).
>
> -Timo
>
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