Re: [PATCH] perf stat: Ignore error thread when enabling system-wide --per-thread

["Jin, Yao" <yao.jin@linux.intel.com>]

Just tested. But looks it's not OK for '--per-thread' case.

jinyao@skl:~/$ ./perf stat --per-thread
WARNING: Ignored open failure for pid 1
WARNING: Ignored open failure for pid 2
WARNING: Ignored open failure for pid 4
WARNING: Ignored open failure for pid 6
WARNING: Ignored open failure for pid 7
WARNING: Ignored open failure for pid 8
WARNING: Ignored open failure for pid 9
WARNING: Ignored open failure for pid 10
......
WARNING: Ignored open failure for pid 11783
WARNING: Ignored open failure for pid 12275
WARNING: Ignored open failure for pid 31733
WARNING: Ignored open failure for pid 31737
Error:
You may not have permission to collect system-wide stats.

Consider tweaking /proc/sys/kernel/perf_event_paranoid,
which controls use of the performance events system by
unprivileged users (without CAP_SYS_ADMIN).

The current value is 2:

   -1: Allow use of (almost) all events by all users
       Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
 >= 0: Disallow ftrace function tracepoint by users without CAP_SYS_ADMIN
       Disallow raw tracepoint access by users without CAP_SYS_ADMIN
 >= 1: Disallow CPU event access by users without CAP_SYS_ADMIN
 >= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN

To make this setting permanent, edit /etc/sysctl.conf too, e.g.:

         kernel.perf_event_paranoid = -1

Thanks
Jin Yao

On 1/16/2018 8:51 PM, Jiri Olsa wrote:
> On Tue, Jan 16, 2018 at 11:43:08PM +0800, Jin Yao wrote:
>> If we execute 'perf stat --per-thread' with non-root account
>> (even set kernel.perf_event_paranoid = -1 yet), it reports the error:
>>
>> jinyao@skl:~$ perf stat --per-thread
>> Error:
>> You may not have permission to collect system-wide stats.
>>
>> Consider tweaking /proc/sys/kernel/perf_event_paranoid,
>> which controls use of the performance events system by
>> unprivileged users (without CAP_SYS_ADMIN).
>>
>> The current value is 2:
>>
>>    -1: Allow use of (almost) all events by all users
>>        Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
>>> = 0: Disallow ftrace function tracepoint by users without CAP_SYS_ADMIN
>>        Disallow raw tracepoint access by users without CAP_SYS_ADMIN
>>> = 1: Disallow CPU event access by users without CAP_SYS_ADMIN
>>> = 2: Disallow kernel profiling by users without CAP_SYS_ADMIN
>>
>> To make this setting permanent, edit /etc/sysctl.conf too, e.g.:
>>
>>          kernel.perf_event_paranoid = -1
>>
>> Perhaps the ptrace rule doesn't allow to trace some processes. But anyway
>> the global --per-thread mode had better ignore such errors and continue
>> working on other threads.
>>
>> This patch will record the index of error thread in perf_evsel__open()
>> and remove this thread before retrying.
>>
>> For example (run with non-root, kernel.perf_event_paranoid isn't set):
>>
>> jinyao@skl:~$ perf stat --per-thread
>> ^C
>>   Performance counter stats for 'system wide':
>>
>>            vmstat-3458               6.171984      cpu-clock:u (msec)        #    0.000 CPUs utilized
>>              perf-3670               0.515599      cpu-clock:u (msec)        #    0.000 CPUs utilized
>>            vmstat-3458              1,163,643      cycles:u                  #    0.189 GHz
>>              perf-3670                 40,881      cycles:u                  #    0.079 GHz
>>            vmstat-3458              1,410,238      instructions:u            #    1.21  insn per cycle
>>              perf-3670                  3,536      instructions:u            #    0.09  insn per cycle
>>            vmstat-3458                288,937      branches:u                #   46.814 M/sec
>>              perf-3670                    936      branches:u                #    1.815 M/sec
>>            vmstat-3458                 15,195      branch-misses:u           #    5.26% of all branches
>>              perf-3670                     76      branch-misses:u           #    8.12% of all branches
>>
>>        12.651675247 seconds time elapsed
> 
> could we use the existing code like in attached patch?
> 
> we might also swap following warning for some generic one:
>    WARNING: Ignored open failure for pid 28392
> 
> jirka
> 
> 
> ---
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 98bf9d32f222..f9d4d3ad6fc5 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -276,6 +276,9 @@ static int create_perf_stat_counter(struct perf_evsel *evsel)
>   			attr->enable_on_exec = 1;
>   	}
>   
> +	if (stat_config.aggr_mode == AGGR_THREAD)
> +		evsel->ignore_missing_thread = true;
> +
>   	if (target__has_cpu(&target) && !target__has_per_thread(&target))
>   		return perf_evsel__open_per_cpu(evsel, perf_evsel__cpus(evsel));
>   
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 8f971a2301d1..509ee175bc97 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1656,7 +1656,7 @@ static bool ignore_missing_thread(struct perf_evsel *evsel,
>   		return false;
>   
>   	/* The -ESRCH is perf event syscall errno for pid's not found. */
> -	if (err != -ESRCH)
> +	if (err != -ESRCH && err != -EACCES)
>   		return false;
>   
>   	/* If there's only one thread, let it fail. */
>