linux-kernel - Re: eMMC low write speed

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Message-ID: <CAHzg1A-p0ygfjTsg8ZRREC_OTXs+k=vMm+zqbvmRm76y9c3veQ@mail.gmail.com>
Date:	Fri, 23 Sep 2011 10:17:07 -0700
From:	Praveen G K <praveen.gk@...il.com>
To:	Timo Kokkonen <kaapeli@...nic.dy.fi>
Cc:	Qiang LIU <godliuqiang@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: eMMC low write speed

On Fri, Sep 23, 2011 at 7:11 AM, Timo Kokkonen <kaapeli@...nic.dy.fi> 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@...il.com> 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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