[PATCH 04/37] perf evsel: Kernel profiling is disallowed only when perf_event_paranoid > 1

From: Arnaldo Carvalho de Melo <acme@kernel•org>
To: Ingo Molnar <mingo@kernel•org>, Thomas Gleixner <tglx@linutronix•de>
Cc: Arnaldo Carvalho de Melo <acme@redhat•com>,
	Mathieu Poirier <mathieu.poirier@linaro•org>,
	Suzuki Poulouse <suzuki.poulose@arm•com>,
	Clark Williams <williams@redhat•com>,
	Alexey Budankov <alexey.budankov@linux•intel.com>,
	Igor Lubashev <ilubashe@akamai•com>,
	linux-kernel@vger•kernel.org, James Morris <jmorris@namei•org>,
	linux-perf-users@vger•kernel.org,
	Alexander Shishkin <alexander.shishkin@linux•intel.com>,
	Peter Zijlstra <peterz@infradead•org>,
	Jiri Olsa <jolsa@kernel•org>, Namhyung Kim <namhyung@kernel•org>,
	linux-arm-kernel@lists•infradead.org
Subject: [PATCH 04/37] perf evsel: Kernel profiling is disallowed only when perf_event_paranoid > 1
Date: Thu, 29 Aug 2019 11:38:44 -0300	[thread overview]
Message-ID: <20190829143917.29745-5-acme@kernel.org> (raw)
In-Reply-To: <20190829143917.29745-1-acme@kernel.org>

From: Igor Lubashev <ilubashe@akamai•com>

Perf was too restrictive about sysctl kernel.perf_event_paranoid. The
kernel only disallows profiling when perf_event_paranoid > 1. Make perf
do the same.

Committer testing:

For a non-root user:

  $ id
  uid=1000(acme) gid=1000(acme) groups=1000(acme),10(wheel) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
  $

Before:

We were restricting it to just userspace (:u suffix) even for a
workload started by the user:

  $ perf record sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.001 MB perf.data (8 samples) ]
  $ perf evlist
  cycles:u
  $ perf evlist -v
  cycles:u: size: 112, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|PERIOD, read_format: ID, disabled: 1, inherit: 1, exclude_kernel: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
  $ perf report --stdio
  # To display the perf.data header info, please use --header/--header-only options.
  #
  # Total Lost Samples: 0
  #
  # Samples: 8  of event 'cycles:u'
  # Event count (approx.): 1040396
  #
  # Overhead  Command  Shared Object     Symbol
  # ........  .......  ................  ......................
  #
      68.36%  sleep    libc-2.29.so      [.] _dl_addr
      27.33%  sleep    ld-2.29.so        [.] dl_main
       3.80%  sleep    ld-2.29.so        [.] _dl_setup_hash
  #
  # (Tip: Order by the overhead of source file name and line number: perf report -s srcline)
  #
  $
  $

After:

When the kernel allows profiling the kernel in that scenario:

  $ perf record sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.023 MB perf.data (11 samples) ]
  $ perf evlist
  cycles
  $ perf evlist -v
  cycles: size: 112, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|PERIOD, read_format: ID, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
  $
  $ perf report --stdio
  # To display the perf.data header info, please use --header/--header-only options.
  #
  # Total Lost Samples: 0
  #
  # Samples: 11  of event 'cycles'
  # Event count (approx.): 1601964
  #
  # Overhead  Command  Shared Object     Symbol
  # ........  .......  ................  ..........................
  #
      28.14%  sleep    [kernel.vmlinux]  [k] __rb_erase_color
      27.21%  sleep    [kernel.vmlinux]  [k] unmap_page_range
      27.20%  sleep    ld-2.29.so        [.] __tunable_get_val
      15.24%  sleep    [kernel.vmlinux]  [k] thp_get_unmapped_area
       1.96%  perf     [kernel.vmlinux]  [k] perf_event_exec
       0.22%  perf     [kernel.vmlinux]  [k] native_sched_clock
       0.02%  perf     [kernel.vmlinux]  [k] intel_bts_enable_local
       0.00%  perf     [kernel.vmlinux]  [k] native_write_msr
  #
  # (Tip: Boolean options have negative forms, e.g.: perf report --no-children)
  #
  $

Reported-by: Arnaldo Carvalho de Melo <acme@redhat•com>
Signed-off-by: Igor Lubashev <ilubashe@akamai•com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat•com>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro•org>
Cc: Alexander Shishkin <alexander.shishkin@linux•intel.com>
Cc: Alexey Budankov <alexey.budankov@linux•intel.com>
Cc: James Morris <jmorris@namei•org>
Cc: Jiri Olsa <jolsa@kernel•org>
Cc: Namhyung Kim <namhyung@kernel•org>
Cc: Peter Zijlstra <peterz@infradead•org>
Cc: Suzuki Poulouse <suzuki.poulose@arm•com>
Cc: linux-arm-kernel@lists•infradead.org
Link: http://lkml.kernel.org/r/1566869956-7154-4-git-send-email-ilubashe@akamai.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat•com>
---
 tools/perf/util/evsel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 7c704b8f0e5c..d4540bfe4574 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -282,7 +282,7 @@ struct evsel *perf_evsel__new_idx(struct perf_event_attr *attr, int idx)
 
 static bool perf_event_can_profile_kernel(void)
 {
-	return perf_event_paranoid_check(-1);
+	return perf_event_paranoid_check(1);
 }
 
 struct evsel *perf_evsel__new_cycles(bool precise)
-- 
2.21.0


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