Re: [PATCH] perf: RISC-V: Check standard event availability

[Atish Patra]

On Wed, Jan 3, 2024 at 8:54 AM Samuel Holland <samuel.holland@xxxxxxxxxx> wrote:
>
> The RISC-V SBI PMU specification defines several standard hardware and
> cache events. Currently, all of these events appear in the `perf list`
> output, even if they are not actually implemented. Add logic to check
> which events are supported by the hardware (i.e. can be mapped to some
> counter), so only usable events are reported to userspace.
>

Thanks for the patch.
This adds tons of SBI calls at every boot for a use case which is at
best confusing for a subset of users who actually wants to run perf.
This probing can be done at runtime by invoking the
pmu_sbi_check_event from pmu_sbi_event_map.
We can update the event map after that so that it doesn't need to
invoke pmu_sbi_check_event next time.

> Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
> ---
> Before this patch:
> $ perf list hw
>
> List of pre-defined events (to be used in -e or -M):
>
>   branch-instructions OR branches                    [Hardware event]
>   branch-misses                                      [Hardware event]
>   bus-cycles                                         [Hardware event]
>   cache-misses                                       [Hardware event]
>   cache-references                                   [Hardware event]
>   cpu-cycles OR cycles                               [Hardware event]
>   instructions                                       [Hardware event]
>   ref-cycles                                         [Hardware event]
>   stalled-cycles-backend OR idle-cycles-backend      [Hardware event]
>   stalled-cycles-frontend OR idle-cycles-frontend    [Hardware event]
>
> $ perf stat -ddd true
>
>  Performance counter stats for 'true':
>
>               4.36 msec task-clock                       #    0.744 CPUs utilized
>                  1      context-switches                 #  229.325 /sec
>                  0      cpu-migrations                   #    0.000 /sec
>                 38      page-faults                      #    8.714 K/sec
>          4,375,694      cycles                           #    1.003 GHz                         (60.64%)
>            728,945      instructions                     #    0.17  insn per cycle
>             79,199      branches                         #   18.162 M/sec
>             17,709      branch-misses                    #   22.36% of all branches
>            181,734      L1-dcache-loads                  #   41.676 M/sec
>              5,547      L1-dcache-load-misses            #    3.05% of all L1-dcache accesses
>      <not counted>      LLC-loads                                                               (0.00%)
>      <not counted>      LLC-load-misses                                                         (0.00%)
>      <not counted>      L1-icache-loads                                                         (0.00%)
>      <not counted>      L1-icache-load-misses                                                   (0.00%)
>      <not counted>      dTLB-loads                                                              (0.00%)
>      <not counted>      dTLB-load-misses                                                        (0.00%)
>      <not counted>      iTLB-loads                                                              (0.00%)
>      <not counted>      iTLB-load-misses                                                        (0.00%)
>      <not counted>      L1-dcache-prefetches                                                    (0.00%)
>      <not counted>      L1-dcache-prefetch-misses                                               (0.00%)
>
>        0.005860375 seconds time elapsed
>
>        0.000000000 seconds user
>        0.010383000 seconds sys
>
> After this patch:
> $ perf list hw
>
> List of pre-defined events (to be used in -e or -M):
>
>   branch-instructions OR branches                    [Hardware event]
>   branch-misses                                      [Hardware event]
>   cache-misses                                       [Hardware event]
>   cache-references                                   [Hardware event]
>   cpu-cycles OR cycles                               [Hardware event]
>   instructions                                       [Hardware event]
>
> $ perf stat -ddd true
>
>  Performance counter stats for 'true':
>
>               5.16 msec task-clock                       #    0.848 CPUs utilized
>                  1      context-switches                 #  193.817 /sec
>                  0      cpu-migrations                   #    0.000 /sec
>                 37      page-faults                      #    7.171 K/sec
>          5,183,625      cycles                           #    1.005 GHz
>            961,696      instructions                     #    0.19  insn per cycle
>             85,853      branches                         #   16.640 M/sec
>             20,462      branch-misses                    #   23.83% of all branches
>            243,545      L1-dcache-loads                  #   47.203 M/sec
>              5,974      L1-dcache-load-misses            #    2.45% of all L1-dcache accesses
>    <not supported>      LLC-loads
>    <not supported>      LLC-load-misses
>    <not supported>      L1-icache-loads
>    <not supported>      L1-icache-load-misses
>    <not supported>      dTLB-loads
>             19,619      dTLB-load-misses
>    <not supported>      iTLB-loads
>              6,831      iTLB-load-misses
>    <not supported>      L1-dcache-prefetches
>    <not supported>      L1-dcache-prefetch-misses
>
>        0.006085625 seconds time elapsed
>
>        0.000000000 seconds user
>        0.013022000 seconds sys
>
>
>  drivers/perf/riscv_pmu_sbi.c | 37 ++++++++++++++++++++++++++++++++++--
>  1 file changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 16acd4dcdb96..b58a70ee8317 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -86,7 +86,7 @@ struct sbi_pmu_event_data {
>         };
>  };
>
> -static const struct sbi_pmu_event_data pmu_hw_event_map[] = {
> +static struct sbi_pmu_event_data pmu_hw_event_map[] = {
>         [PERF_COUNT_HW_CPU_CYCLES]              = {.hw_gen_event = {
>                                                         SBI_PMU_HW_CPU_CYCLES,
>                                                         SBI_PMU_EVENT_TYPE_HW, 0}},
> @@ -120,7 +120,7 @@ static const struct sbi_pmu_event_data pmu_hw_event_map[] = {
>  };
>
>  #define C(x) PERF_COUNT_HW_CACHE_##x
> -static const struct sbi_pmu_event_data pmu_cache_event_map[PERF_COUNT_HW_CACHE_MAX]
> +static struct sbi_pmu_event_data pmu_cache_event_map[PERF_COUNT_HW_CACHE_MAX]
>  [PERF_COUNT_HW_CACHE_OP_MAX]
>  [PERF_COUNT_HW_CACHE_RESULT_MAX] = {
>         [C(L1D)] = {
> @@ -265,6 +265,36 @@ static const struct sbi_pmu_event_data pmu_cache_event_map[PERF_COUNT_HW_CACHE_M
>         },
>  };
>
> +static void pmu_sbi_check_event(struct sbi_pmu_event_data *edata)
> +{
> +       struct sbiret ret;
> +
> +       ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_CFG_MATCH,
> +                       0, cmask, 0, edata->event_idx, 0, 0);
> +       if (!ret.error) {
> +               sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP,
> +                         ret.value, 0x1, SBI_PMU_STOP_FLAG_RESET, 0, 0, 0);
> +       } else if (ret.error == SBI_ERR_NOT_SUPPORTED) {
> +               /* This event cannot be monitored by any counter */
> +               edata->event_idx = -EINVAL;
> +       }
> +}
> +
> +static void pmu_sbi_update_events(void)
> +{
> +       /* Ensure events are not already mapped to a counter */
> +       sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP,
> +                 0, cmask, SBI_PMU_STOP_FLAG_RESET, 0, 0, 0);
> +
> +       for (int i = 0; i < ARRAY_SIZE(pmu_hw_event_map); i++)
> +               pmu_sbi_check_event(&pmu_hw_event_map[i]);
> +
> +       for (int i = 0; i < ARRAY_SIZE(pmu_cache_event_map); i++)
> +               for (int j = 0; j < ARRAY_SIZE(pmu_cache_event_map[i]); j++)
> +                       for (int k = 0; k < ARRAY_SIZE(pmu_cache_event_map[i][j]); k++)
> +                               pmu_sbi_check_event(&pmu_cache_event_map[i][j][k]);
> +}
> +
>  static int pmu_sbi_ctr_get_width(int idx)
>  {
>         return pmu_ctr_list[idx].width;
> @@ -1046,6 +1076,9 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>         if (pmu_sbi_get_ctrinfo(num_counters, &cmask))
>                 goto out_free;
>
> +       /* Check which standard events are available */
> +       pmu_sbi_update_events();
> +
>         ret = pmu_sbi_setup_irqs(pmu, pdev);
>         if (ret < 0) {
>                 pr_info("Perf sampling/filtering is not supported as sscof extension is not available\n");
> --
> 2.42.0
>


--
Regards,
Atish