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

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Date:   Tue, 23 Nov 2021 09:25:59 -0600
From:   Kim Phillips <kim.phillips@....com>
To:     kajoljain <kjain@...ux.ibm.com>, Jiri Olsa <jolsa@...hat.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Ian Rogers <irogers@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Michael Petlan <mpetlan@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Robert Richter <robert.richter@....com>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/2] perf tools: Improve IBS error handling

On 11/23/21 2:40 AM, kajoljain wrote:
> 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.");
> +            }

IIRC, I tried something like that but carrying the


struct target *target, int err, char *msg, size_t size

parameters made things worse.

> 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.

The vast majority of decisions made by evsel__open_strerror are
going to be common across most arch/uarches.  AMD has only these
two pesky exceptions to the rule and therefore IMO it's ok
to have them inline with the common function, since the decisions
are so deeply intertwined.  A new amd_evsel_open_strerror_check
sounds like it'd duplicate too much of the common function code
in order to handle the common error cases.

Kim