Re: [PATCH 2/2] perf tools: Improve IBS error handling

kajoljain
2021-11-23T08:41:16Z

On 10/8/21 12:47 AM, Kim Phillips wrote:
> On 10/7/21 12:28 PM, Jiri Olsa wrote:
>> On Mon, Oct 04, 2021 at 04:41:14PM -0500, Kim Phillips wrote:
>>> ---
>>>   tools/perf/util/evsel.c | 24 ++++++++++++++++++++++++
>>>   1 file changed, 24 insertions(+)
>>>
>>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>>> index b915840690d4..f8a9cbd99314 100644
>>> --- a/tools/perf/util/evsel.c
>>> +++ b/tools/perf/util/evsel.c
>>> @@ -2743,9 +2743,22 @@ static bool find_process(const char *name)
>>>       return ret ? false : true;
>>>   }
>>>   +static bool is_amd(const char *arch, const char *cpuid)
>>> +{
>>> +    return arch && !strcmp("x86", arch) && cpuid && strstarts(cpuid,
>>> "AuthenticAMD");
>>> +}
>>> +
>>> +static bool is_amd_ibs(struct evsel *evsel)
>>> +{
>>> +    return evsel->core.attr.precise_ip || !strncmp(evsel->pmu_name,
>>> "ibs", 3);
>>> +}
>>> +
>>>   int evsel__open_strerror(struct evsel *evsel, struct target *target,
>>>                int err, char *msg, size_t size)
>>>   {
>>> +    struct perf_env *env = evsel__env(evsel);
>>> +    const char *arch = perf_env__arch(env);
>>> +    const char *cpuid = perf_env__cpuid(env);
>>>       char sbuf[STRERR_BUFSIZE];
>>>       int printed = 0, enforced = 0;
>>>   @@ -2841,6 +2854,17 @@ int evsel__open_strerror(struct evsel
>>> *evsel, struct target *target,
>>>               return scnprintf(msg, size, "wrong clockid (%d).",
>>> clockid);
>>>           if (perf_missing_features.aux_output)
>>>               return scnprintf(msg, size, "The 'aux_output' feature
>>> is not supported, update the kernel.");
>>> +        if (is_amd(arch, cpuid)) {
>>> +            if (is_amd_ibs(evsel)) {
>>
>> would single 'is_amd_ibs' call be better? checking on both amd and ibs
>
> Good suggestion. If you look at the later patch in the
> BRS series, I have rewritten it to add the new
> AMD PMU like so:
>
>  if (is_amd()) {
>      if (is_amd_ibs()) {
>          if (evsel->this)
>              return
>          if (evsel->that)
>              return
>      }
> +    if (is_amd_brs()) {
> +        if (evsel->this)
> +            return
> +        if (evsel->that)
> +            return
> +    }
>  }

Hi Kim,
From my point of view, it won't be a good idea of adding so many
checks in common function definition itself.

Can you just create a check to see if its amd machine and then add a
function call which will handle all four conditions together?

which is basically for:

+ if (is_amd(arch, cpuid)) {
+ if (is_amd_ibs(evsel)) {
+ if (evsel->core.attr.exclude_kernel)
+ return scnprintf(msg, size,
+ "AMD IBS can't exclude kernel events. Try running at a higher
privilege level.");
+ if (!evsel->core.system_wide)
+ return scnprintf(msg, size,
+ "AMD IBS may only be available in system-wide/per-cpu mode. Try using
-a, or -C and workload affinity");
+ }

and this:

+ if (is_amd_brs(evsel)) {
+ if (evsel->core.attr.freq)
+ return scnprintf(msg, size,
+ "AMD Branch Sampling does not support frequency mode sampling, must
pass a fixed sampling period via -c option or
cpu/branch-brs,period=xxxx/.");
+ /* another reason is that the period is too small */
+ return scnprintf(msg, size,
+ "AMD Branch Sampling does not support sampling period smaller than
what is reported in /sys/devices/cpu/caps/branches.");
+ }

So, incase we are in amd machine, common function evsel__open_strerror
will call function may be something like amd_evesel_open_strerror_check
which will look for both ibs and brs conditions and return corresponding
error statement.

Thanks,
Kajol Jain

>
> Below is the full proposed replacement patch for patch 12
> of 13 of the BRS series.
>
> Another option is to have the is_amd_{ibs,brs} functions
> call is_amd() themselves, so the if (evsel->) code could be
> unindented by one tab, would that be better?
>
> Thanks,
>
> Kim
>
> From a4cbab762719b30bddec2e278cf8b8eb82e83865 Mon Sep 17 00:00:00 2001
> From: Stephane Eranian <eranian@google.com>
> Date: Thu, 9 Sep 2021 00:56:59 -0700
> Subject: [PATCH] perf tools: Improve error handling of AMD Branch Sampling
>
> This patch improves the error message printed by perf when
> perf_event_open() fails on AMD Zen3 when using the branch sampling
> feature. In the case of EINVAL, there are two main reasons: frequency
> mode or period is smaller than the depth of the branch sampling
> buffer (16). The patch checks the parameters of the call and tries
> to print a relevant message to explain the error:
>
> $ perf record -b -e cpu/branch-brs/ -c 10 ls
> Error:
> AMD Branch Sampling does not support sampling period smaller than what
> is reported in /sys/devices/cpu/caps/branches.
>
> $ perf record -b -e cpu/branch-brs/ ls
> Error:
> AMD Branch Sampling does not support frequency mode sampling, must pass
> a fixed sampling period via -c option or cpu/branch-brs,period=xxxx/.
>
> Signed-off-by: Stephane Eranian <eranian@google.com>
> [Rebased on commit 9fe8895a27a84 ("perf env: Add perf_env__cpuid,
> perf_env__{nr_}pmu_mappings")]
> Signed-off-by: Kim Phillips <kim.phillips@amd.com>
> ---
>  tools/perf/util/evsel.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index f8a9cbd99314..e1f5eff07355 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2753,6 +2753,12 @@ static bool is_amd_ibs(struct evsel *evsel)
>      return evsel->core.attr.precise_ip || !strncmp(evsel->pmu_name,
> "ibs", 3);
>  }
>
> +static bool is_amd_brs(struct evsel *evsel)
> +{
> +    return ((evsel->core.attr.config & 0xff) == 0xc4) &&
> +           (evsel->core.attr.sample_type & PERF_SAMPLE_BRANCH_STACK);
> +}
> +
>  int evsel__open_strerror(struct evsel *evsel, struct target *target,
>               int err, char *msg, size_t size)
>  {
> @@ -2863,6 +2869,14 @@ int evsel__open_strerror(struct evsel *evsel,
> struct target *target,
>                      return scnprintf(msg, size,
>      "AMD IBS may only be available in system-wide/per-cpu mode.  Try
> using -a, or -C and workload affinity");
>              }
> +            if (is_amd_brs(evsel)) {
> +                if (evsel->core.attr.freq)
> +                    return scnprintf(msg, size,
> +    "AMD Branch Sampling does not support frequency mode sampling, must
> pass a fixed sampling period via -c option or
> cpu/branch-brs,period=xxxx/.");
> +                /* another reason is that the period is too small */
> +                return scnprintf(msg, size,
> +    "AMD Branch Sampling does not support sampling period smaller than
> what is reported in /sys/devices/cpu/caps/branches.");
> +            }
>          }
>
>          break;