linux-kernel - Re: [PATCH] perf evsel amd: Fix IBS error message

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Date:   Thu, 22 Jun 2023 10:57:57 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     acme@...nel.org, peterz@...radead.org, irogers@...gle.com,
        jolsa@...nel.org, adrian.hunter@...el.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        sandipan.das@....com, ananth.narayan@....com,
        santosh.shukla@....com, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH] perf evsel amd: Fix IBS error message

Hi Namhyung,

On 22-Jun-23 4:03 AM, Namhyung Kim wrote:
> Hi Ravi,
> 
> On Tue, Jun 20, 2023 at 11:24 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
>>
>> AMD IBS can do per-process profiling[1] and is no longer restricted to
>> per-cpu or systemwide only. Remove stale error message.
>>
>> Before:
>>   $ sudo ./perf record -e "{ibs_op//,ibs_op//}" -C 0
>>   Error:
>>   AMD IBS may only be available in system-wide/per-cpu mode.
>>   Try using -a, or -C and workload affinity
> 
> It was strange that the -C option was given already.

Hmm. evsel->core.system_wide is bit confusing for me. A Comment on it's
definition says "irrespective of user requested CPUs or threads":

        /*
         * system_wide is for events that need to be on every CPU, irrespective
         * of user requested CPUs or threads. Map propagation will set cpus to
         * this event's own_cpus, whereby they will contribute to evlist
         * all_cpus.
         */
        bool                     system_wide;

So, I guess evsel->core.system_wide doesn't depend on -a / -C.

> 
>>
>> After:
>>   $ sudo ./perf record -e "{ibs_op//,ibs_op//}" -C 0
>>   Error:
>>   The sys_perf_event_open() syscall returned with 22 (Invalid
>>   argument) for event (ibs_op//).
>>   /bin/dmesg | grep -i perf may provide additional information.
> 
> It can run newer perf tools on an old kernel but the old error
> message seems to be invalid anyway.  So I'm ok with removing it.

Right.

>>
>> [1] https://git.kernel.org/torvalds/c/30093056f7b2
>>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
>> ---
>>  tools/perf/util/evsel.c | 10 +++-------
>>  1 file changed, 3 insertions(+), 7 deletions(-)
>>
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 356c07f03be6..65b0b70830f0 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -3092,14 +3092,10 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
>>                         return scnprintf(msg, size,
>>         "Invalid event (%s) in per-thread mode, enable system wide with '-a'.",
>>                                         evsel__name(evsel));
>> -               if (is_amd(arch, cpuid)) {
>> -                       if (is_amd_ibs(evsel)) {
>> -                               if (evsel->core.attr.exclude_kernel)
>> -                                       return scnprintf(msg, size,
>> +               if (is_amd(arch, cpuid) && 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.");
> 
> I'm not sure if it's enough.  The IBS PMUs have CAP_NO_EXCLUDE then
> it can't exclude user events too, right?

That's correct. Let me try to fix this whole `if (is_amd())` part properly.

Thanks for your feedback,
Ravi