On Thu, Jan 28, 2016 at 02:38:16PM +0000, Mathieu Desnoyers wrote: > ----- On Jan 28, 2016, at 8:57 AM, Peter Zijlstra [email protected] wrote: > > > On Thu, Jan 28, 2016 at 01:38:00PM +0000, Mathieu Desnoyers wrote: > > > >> Thoughts ? > > > > So ideally dumping the trace data would not depend on any of that, > > because I can break it all :-) > > > > Not being able to access the trace data completely and utterly defeats > > the purpose of having a tracer in the first place. > > One item I have on my todo list is to allow mapping > the tracer buffers (lttng in my case) onto RAM that > persists across reboots/kexec using dax and the pmem > driver. Since the original system is clearly inactive > after a reboot, we can read the buffers from memory > without caring about synchronization.
I would expect the new kernel to use the same buffer for its tracing, right? After all, there's no distinction between the old and new kernel except a reboot. In which case, my kernels often start babbling the moment I boot. So I need to take care not to scribble the old data. > That would be one possible way of handling your > snapshot-of-buggy-kernel-trace-buffers use-case. Now I wonder if my ipmipower -r is a warn reset :-) (I'm assuming the pmem/dax stuff would simply use regular RAM to back this stuff)
