Re: LBR callchains from tracepoints

[Peter Zijlstra]

On Mon, Apr 25, 2016 at 10:24:31PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Apr 25, 2016 at 10:03:58PM -0300, Arnaldo Carvalho de Melo escreveu:
> > I now need to continue investigation why this doesn't seem to work from
> > tracepoints...
> 
> Bummer, the changeset (at the end of this message) hasn't any
> explanation, is this really impossible? I.e. LBR callstacks from
> tracepoints? Even if we set perf_event_attr.exclude_callchain_kernel?

Could maybe be done, but its tricky to implement as the LBR is managed
by the hardware PMU and tracepoints are a software PMU, so we need to
then somehow frob with cross-pmu resources, in a very arch specific way.
And programmability of the hardware PMU will then depend on events
outside of it.

All rather icky.