Re: [PATCH v2] perf stat: Include PMU name and split uncore events per PMU in metric-only JSON output

[Namhyung Kim <namhyung@kernel.org>]

On Wed, Jul 15, 2026 at 08:15:46PM -0700, Ian Rogers wrote:
> On Wed, Jul 15, 2026 at 1:30 PM Chun-Tse Shao <ctshao@google.com> wrote:
> >
> > When running `perf stat` with `-A` (--no-aggr) and `--metric-only` in
> > JSON output mode (`-j`), `perf stat` evaluates metric expressions
> > across all matching PMUs (including uncore PMUs like `uncore_iio_0`,
> > `uncore_iio_1`, etc.).
> >
> > However, `perf stat` previously formatted JSON output by printing only
> > "cpu" : "<id>" and grouping all metric values on a single line per CPU
> > without identifying which PMU instance evaluated each metric. As a
> > result, when an uncore event spans multiple PMU boxes, `perf stat`
> > printed repeated, ambiguous metric keys without PMU names.
> >
> > Fix this by:
> > 1. Including "pmu" : "<pmu_name>" in print_aggr_id_json when evsel->pmu
> >    is a non-core or hybrid PMU in AGGR_NONE mode (-A).
> > 2. Starting a new JSON metric line in AGGR_NONE mode (-A) whenever the
> >    underlying PMU instance changes across PMU events.
> > 3. Updating perf_json_output_lint.py to recognize the new "pmu" key in
> >    the JSON test suite.
> >
> > Example output:
> >   $ perf stat -M iio_bandwidth_read -a -A --metric-only -j -I 1000
> >   {"interval" : 1.000314908, "cpu" : "0", "pmu" : "uncore_iio_0", "MB/s  iio_bandwidth_read" : "0.0"}
> >   {"interval" : 1.000314908, "cpu" : "0", "pmu" : "uncore_iio_1", "MB/s  iio_bandwidth_read" : "0.1"}
> >   {"interval" : 1.000314908, "cpu" : "0", "pmu" : "uncore_iio_11", "MB/s  iio_bandwidth_read" : "0.0"}
> >   ...
> >   {"interval" : 1.000314908, "cpu" : "56", "pmu" : "uncore_iio_0", "MB/s  iio_bandwidth_read" : "0.0"}
> >   {"interval" : 1.000314908, "cpu" : "56", "pmu" : "uncore_iio_1", "MB/s  iio_bandwidth_read" : "0.0"}
> >   {"interval" : 1.000314908, "cpu" : "56", "pmu" : "uncore_iio_11", "MB/s  iio_bandwidth_read" : "0.0"}
> >
> > Signed-off-by: Chun-Tse Shao <ctshao@google.com>
> > Assisted-by: Gemini:gemini-3.1-pro-preview
> 
> Reviewed-by: Ian Rogers <irogers@google.com>
> 
> Nit: It may be nice to include the before output (i.e., without the
> PMU showing that differentiation isn't possible) in the commit
> message.

Hi CT, can you please update the commit message?  It'd be very helpful
for others to understand the problem.

Thanks,
Namhyung