Re: [PATCH v4 0/9] perf report/top: Add opt-in --hybrid-merge

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Wed, Sep 16, 2026 at 10:06:59PM -0700, Ian Rogers wrote:
> On a hybrid machine a wildcard event expands to one event per core
> PMU, so "perf record -e cycles" records cpu_core/cycles/ and
> cpu_atom/cycles/. perf report and perf top then show one histogram per
> PMU, and a symbol that ran on both kinds of core is split across them,
> with each percentage relative to its own PMU's total. There is no way
> to ask for the single combined profile.
> 
> Add --hybrid-merge to perf report and perf top, which merges the
> histograms of the events that came from the same wildcard into one,
> with percentages taken against the summed period.
> 
> Merging is opt-in because it isn't always the right thing to do. The
> cores differ in performance, so a merged cycles count mixes work done
> at different rates and a merged IPC is not the IPC of either core
> type. perf-tips notes this. When merging is possible but wasn't asked
> for, the TUI says so, rather than merging silently.
> 
> core.hybrid-merge in .perfconfig turns it on by default. As a default
> rather than an explicit request it yields to the command line: with
> --hierarchy it is ignored with a warning, whereas asking for both
> --hierarchy and --hybrid-merge on the command line is an error. For
> the same reason it is silent when there is nothing to merge, so it
> doesn't warn on every invocation on a machine with a single core PMU.
> 
> perf stat is deliberately untouched. Counting already has its own
> merging options, and this is aimed at sampling.
> 
> The events to merge are found with first_wildcard_match, which parsing
> fills in. perf report reads events from a file rather than parsing
> them, so there the wildcard grouping is recovered by matching event
> names, and core PMUs are identified from the perf.data header topology
> so that a file recorded on another machine is read correctly.

Thanks, applied to perf-tools-next, for v7.4.

- Arnaldo