Re: [RFC v2 0/6] x86: dynamic indirect branch promotion

[Peter Zijlstra]

On Thu, Jan 03, 2019 at 02:18:15PM -0800, Andi Kleen wrote:
> Nadav Amit <namit@xxxxxxxxxx> writes:
> >
> > - Do we use periodic learning or not? Josh suggested to reconfigure the
> >   branches whenever a new target is found. However, I do not know at
> >   this time how to do learning efficiently, without making learning much
> >   more expensive.
> 
> FWIW frequent patching will likely completely break perf Processor Trace
> decoding, which needs a somewhat stable kernel text image to decode the
> traces generated by the CPU. Right now it relies on kcore dumped after
> the trace usually being stable because jumplabel changes happen only
> infrequently. But if you start patching frequently this assumption will
> break.
> 
> You would either need a way to turn this off, or provide
> updates for every change to the trace, so that the decoder can
> keep track.

I'm thining it would be entirely possible to create and feed text_poke
events into the regular (!aux) buffer which can be timestamp correlated
to the PT data.