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

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Date:   Tue, 16 Jan 2018 13:51:32 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Jin Yao <yao.jin@...ux.intel.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH] perf stat: Ignore error thread when enabling system-wide
 --per-thread

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. */