Problem writing to SD card

António Silva silva.antonio at gmail.com
Wed Sep 17 06:20:09 CDT 2008


Hi Jon,

In fact with the "old" LSP and with 4G SD card, at /proc/meminfo I verify
that  Dirty is climbing from 0 until my application hangs at 50000KB.

I also verified that when the application hangs, it tries to write some of
this buffered data to the card (Dirty begins to fall) and then it starts
running again shortly and then hangs again.

Regarding Writeback it's value does not climb as with Dirty, it is around
115K. When the application hangs Writeback pass to 0 temporally.

This must be a throughput problem.

I will test with the latest LSP and with the SDHC card to see if the results
are the same.

Best Regards,

A.Silva


On Fri, Sep 12, 2008 at 9:14 AM, Jon Povey <Jon.Povey at racelogic.co.uk>wrote:

> > I believe I was able to do this without locking up, but I had
> > to use the SDIO driver in patch set 45 and an SDHC class6
> > device to get higher throughput.  I think Chris is correct
> > about you not having enough throughput.
>
> If you cat /proc/meminfo, have a look at the "Dirty:" and "Writeback:"
> lines when your app starts running and then as it starts to stall. On a
> MIPS-based emebedded linux system I used this to see that I could not write
> to card fast enough, the Writeback: line would keep growing: these are the
> pages the kernel is actively trying to write out. Dirty: are pages that are
> written but buffered and not trying to be written yet.
>
> Not sure it is the same on DM355 but worth a look. If Writeback: starts
> climbing and you app then stalls I would point the finger at write
> throughput.
>
> --
> Jon Povey, Design Engineer
> jon.povey at racelogic.co.uk | +44(0)1280 825983
>
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