Re: [PATCH v1 2/2] perf script: Fix for `perf script +F metric` with leader sampling

[James Clark <james.clark@linaro.org>]

On 20/07/2024 8:45 am, Ian Rogers wrote:
> Andi Kleen reported a regression where `perf script +F metric` would
> crash. With this change the output is:
> 
> ```
> $ perf record -a -e '{cycles,instructions}:S' perf bench mem memcpy
> 
>        21.229620 GB/sec
> 
>        15.751008 GB/sec
> 
>        16.009221 GB/sec
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 1.945 MB perf.data (294 samples) ]
> $ perf --no-pager script -F +metric
>              perf 1912464 [000] 814503.473101:       6325       cycles:  ffffffff8548d64a native_write_msr+0xa ([kernel.kallsyms])
>              perf 1912464 [000] 814503.473101:   metric:    0.06  insn per cycle
>              perf 1912464 [000] 814503.473101:        351 instructions:  ffffffff8548d64a native_write_msr+0xa ([kernel.kallsyms])
>              perf 1912464 [000] 814503.473101:   metric:    0.03  insn per cycle
> ...
> ```

For some reason I only get the metric: lines when I record with -a. I 
noticed this because Andi's test doesn't use -a so it fails.

I'm not sure if that's expected or it's related to your disclaimer below?

> 
> The change fixes perf script to update counts and thereby aggregate
> values which then get consumed by unchanged metric logic in the shadow
> stat output. Note, it would be preferential to switch to json metrics.
> 
> Reported-by: Andi Kleen <ak@linux.intel.com>
> Closes: https://lore.kernel.org/linux-perf-users/20240713155443.1665378-1-ak@linux.intel.com/
> Fixes: 37cc8ad77cf8 ("perf metric: Directly use counts rather than saved_value")'
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> The code isn't well tested nor does it support non-leader sampling
> reading of counts based on periods that seemed to present in the
> previous code. Sending out for the sake of discussion. Andi's changes
> added a test and that should certainly be added.
> ---
>   tools/perf/builtin-script.c | 114 +++++++++++++++++++++++++++++-------
>   1 file changed, 93 insertions(+), 21 deletions(-)
>