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SubjectRe: [RFC v2 0/6] x86: dynamic indirect branch promotion
On Thu, Jan 03, 2019 at 02:18:15PM -0800, Andi Kleen wrote:
> Nadav Amit <namit@vmware.com> 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.

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