Re: [PATCH v2 3/5] perf cs-etm: Add branch history to existing samples

[sashiko-bot@kernel.org]

> Implement --itrace=L for CoreSight ETM: decode timestamped trace up to
> each existing PMU sample and attach the branch history that led to it.
> The sample keeps its own ip, callchain and event identity, and a sample
> that already carries a branch stack is left alone.
> 
> Samples are correlated with the trace by time, so this requires virtual
> ETM timestamps that are correlated to perf time; timeless decoding is
> rejected. The decode loop, which the previous patch left on its own in
> cs_etm__process_timestamped_queues(), grows a timestamp argument and
> stops once the decode frontier reaches it, so on return the
> thread stack holds the branches that executed before the sample and none
> that executed after. Attaching then reduces to the same
> thread_stack__br_sample_late() call intel-pt uses.
> 
> No explicit sample-to-queue matching is needed:
> [ ... ]
> can actually return n entries. Kernel-inclusive trace gets the same
> conservative 1024-entry headroom that intel-pt uses.
> 
> Assisted-by: Devmate:GPT-5.6
> Signed-off-by: Amir Ayupov <aaupov@fb.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/cover.1787005265.git.aaupov@fb.com?part=3