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

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

On Fri, Sep 18, 2026 at 05:40:15PM -0300, Arnaldo Carvalho de Melo wrote:
> 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.

I tried 'perf top --hybrid-merge" on this machine:

acme@x2:~/git/perf-tools-next$ grep -m1 "model name" /proc/cpuinfo
model name	: Intel(R) Core(TM) i7-8650U CPU @ 1.90GHz
acme@x2:~/git/perf-tools-next$

That is hybrid and it didn't merge anything, just told me that:

                       ┌─Warning:──────────────────────────────────────────┐
                       │--hybrid-merge: no events to merge across core PMUs│
                       │                                                   │
                       │                                                   │
                       │Press any key...                                   │
                       └───────────────────────────────────────────────────┘

What am I missing?

I merged this, so we can continue from there,

- Arnaldo