[Ce-android-mainline] ram console

[Todd Poynor]

On Wed, Jan 18, 2012 at 7:00 PM, Tim Bird <tim.bird at am.sony.com> wrote:
...
> Does pstore or ramoops have any error correction capability, like
> ram console?  I presume this is to help ameliorate problems with RAM
> degradation over a reboot, but does anyone know.  Is this turned
> on by default for ram console in Android devices?  Is ram console
> enabled on production devices, or only during development?
> (I don't know if you know the answers to these, but it might
> help understand the common Android use case if we can find out.)

ramconsole is enabled on production devices and is used to diagnose
panics and watchdog resets in the field.  Assuming it's not disabled
by the OEM, Android devices have facilities for taking bug reports
that include copying out the contents of /proc/last_kmsg.

Yes, the ECC features are used to detect, and usually correct, memory
errors that commonly occur during the warm reset of many platforms.

> Personally, I prefer the ram console approach to saving messages,
> as it more closely matches what how the serial console works,
> and also saves messages in cases where the kernel doesn't even
> panic correctly (though these are probably rare).

Unfortunately, freezes followed by watchdog resets aren't always
terribly rare (hopefully mainly during the development phase, but it's
(ahem) not unheard of to be plagued by these after release).

Patches have also been floated that generalize ramconsole to a
persistent memory area that also stores general < key, value > pairs
set by the the previous boot of the kernel for debugging specific
problems.


Todd