Messages in this thread | | | Date | Fri, 23 Sep 2011 10:17:07 -0700 | Subject | Re: eMMC low write speed | From | Praveen G K <> |
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On Fri, Sep 23, 2011 at 7:11 AM, Timo Kokkonen <kaapeli@itanic.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@gmail.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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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