Messages in this thread | | | Subject | Re: [PATCH 11/13] android: persistent_trace: ftrace into persistent_ram | From | John Stultz <> | Date | Wed, 07 Mar 2012 14:40:54 -0800 |
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On Wed, 2012-03-07 at 14:10 -0800, Greg KH wrote: > On Wed, Mar 07, 2012 at 01:58:21PM -0800, John Stultz wrote: > > From: Colin Cross <ccross@android.com> > > > > persistent_trace uses the ftrace infrastructure, but traces > > into a persistent_ram buffer instead of the regular ftrace > > ringbuffer. After a reset or panic, the trace can be > > decoded with cat /sys/kernel/debug/persistent_trace. > > Has this patch been run by the tracing kernel developers?
Probably not. If you'd prefer, we can drop this one and come back to it later.
> And what's the status on merging the persistent_ram stuff in with the > in-kernel api for this type of thing? That should then get rid of this > separate tracing module, or at the least, let it be accepted directly by > the tracing developers and not need to go through staging, right?
From my understanding, ram_console/persistent_ram functionality isn't really the same as pstore/ramoops.
When asked earlier about this, Colin said: "pstore is just an interface to write to a persistent storage, with a tiny driver on it to dump console messages after a panic. With the number of crashes we see on ARM cpus that are not panics (mostly watchdog resets), logging only after a panic is not appropriate, so it can't replace ramconsole. persistent_ram could easily be a pstore driver, but that would not give any new useful functionality, since ramconsole is better for us than pstore_dump.
Looking at ramoops, it is exactly the same as pstore on ioremapped ram, but was originally implemented separately. I see patches now that convert it to a pstore backend, which leaves us in the same state as above - only logging panics."
As for the long term merging story, I think Colin's idea of using persistent_ram a backing for pstore, then adapting pstore as needed to provide similar continuous console logging like ram_console might be a way forward, but I don't know of anyone actively working on that atm.
Tony: Do you have any thoughts here?
thanks -john
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