Re: [QUESTION] Is there a better way to get ftrace dump on guest?

Namhyung Kim
2016-06-29T00:53:07Z

Hi Steve,

On Tue, Jun 28, 2016 at 09:57:27AM -0400, Steven Rostedt wrote:
> On Tue, 28 Jun 2016 15:33:18 +0900
> Namhyung Kim <namhyung@kernel.org> wrote:
>
> > Send again to correct addresses, sorry!
> >
> > On Tue, Jun 28, 2016 at 3:25 PM, Namhyung Kim <namhyung@kernel.org> wrote:
> > > Hello,
> > >
> > > I'm running some guest machines for kernel development. For debugging
> > > purpose, I use lots of trace_printk() since it's faster than normal
> > > printk(). When kernel crash happens the trace buffer is printed on
> > > console (I set ftrace_dump_on_oops) but it takes too much time. I
> > > don't want to reduce the size of ring buffer as I want to collect the
> > > debug info as much as possible. And I also want to see trace from all
> > > cpu so 'ftrace_dump_on_oop = 2' is not an option.
> > >
> > > I know the kexec/kdump (and the crash tool) can dump and analyze the
> > > trace buffer later. But it's cumbersome to do it everytime and more
> > > importantly, I don't want to spend the memory for the crashkernel.
> > >
> > > So what is the best way to handle this? I'd like to know how others
> > > setup the debugging environment..
>
> Heh, I'd say something helpful but you basically already shot down all
> of my advice, because what I do is...
>
> 1) Reduce the size of the ring buffer
>
> 2) Dump out just one CPU
>
> 3) use kexec/kdump and make a crash kernel to extract trace.dat from
>
>
> That's my debugging environment, but it looks like you want something
> else.

Thanks for sharing. Yeah, I'd like to know other ways to overcome
this if possible. Since I don't have enough knowledge about this
area, I hope others would have better idea. :)

Thanks,
Namhyung