perf record: Respect --no-switch-events

Context switch events are added automatically by Intel PT and Coresight.

Make it possible to suppress them. That is useful for tracing the
scheduler without the disturbance that the switch event processing
creates.

Example:

  Prerequisites:

    $ which perf
    ~/bin/perf
    $ sudo setcap "cap_sys_rawio,cap_sys_admin,cap_sys_ptrace,cap_syslog,cap_ipc_lock=ep" ~/bin/perf
    $ sudo chmod +r /proc/kcore

  Before:

    $ perf record --no-switch-events --kcore -a -e intel_pt//k -- sleep 0.001
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.938 MB perf.data ]
    $ perf script -D | grep PERF_RECORD_SWITCH | wc -l
    572

  After:

    $ perf record --no-switch-events --kcore -a -e intel_pt//k -- sleep 0.001
    Warning:
    Intel Processor Trace decoding will not be possible except for kernel tracing!
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.838 MB perf.data ]
    $ perf script -D | grep PERF_RECORD_SWITCH | wc -l
    0

    $ sudo chmod go-r /proc/kcore
    $ sudo setcap -r ~/bin/perf

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: http://lore.kernel.org/lkml/20200528120859.21604-1-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 561ef55..97b1a86 100644 (file)
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -458,7 +458,9 @@ This option sets the time out limit. The default value is 500 ms.
 
 --switch-events::
 Record context switch events i.e. events of type PERF_RECORD_SWITCH or
-PERF_RECORD_SWITCH_CPU_WIDE.
+PERF_RECORD_SWITCH_CPU_WIDE. In some cases (e.g. Intel PT or CoreSight)
+switch events will be enabled automatically, which can be suppressed by
+by the option --no-switch-events.
 
 --clang-path=PATH::
 Path to clang binary to use for compiling BPF scriptlets.

diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
index 607499b..cea5e33 100644 (file)
--- a/tools/perf/arch/arm/util/cs-etm.c
+++ b/tools/perf/arch/arm/util/cs-etm.c
@@ -265,7 +265,8 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
        ptr->evlist = evlist;
        ptr->snapshot_mode = opts->auxtrace_snapshot_mode;
 
-       if (perf_can_record_switch_events())
+       if (!record_opts__no_switch_events(opts) &&
+           perf_can_record_switch_events())
                opts->record_switch_events = true;
 
        evlist__for_each_entry(evlist, evsel) {

diff --git a/tools/perf/arch/x86/util/intel-pt.c b/tools/perf/arch/x86/util/intel-pt.c
index 0fe401a..de69c8a 100644 (file)
--- a/tools/perf/arch/x86/util/intel-pt.c
+++ b/tools/perf/arch/x86/util/intel-pt.c
@@ -787,7 +787,8 @@ static int intel_pt_recording_options(struct auxtrace_record *itr,
         * Per-cpu recording needs sched_switch events to distinguish different
         * threads.
         */
-       if (have_timing_info && !perf_cpu_map__empty(cpus)) {
+       if (have_timing_info && !perf_cpu_map__empty(cpus) &&
+           !record_opts__no_switch_events(opts)) {
                if (perf_can_record_switch_events()) {
                        bool cpu_wide = !target__none(&opts->target) &&
                                        !target__has_task(&opts->target);

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index c69f163..ecd478a 100644 (file)
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -2501,8 +2501,9 @@ static struct option __record_options[] = {
                    "Record namespaces events"),
        OPT_BOOLEAN(0, "all-cgroups", &record.opts.record_cgroup,
                    "Record cgroup events"),
-       OPT_BOOLEAN(0, "switch-events", &record.opts.record_switch_events,
-                   "Record context switch events"),
+       OPT_BOOLEAN_SET(0, "switch-events", &record.opts.record_switch_events,
+                       &record.opts.record_switch_events_set,
+                       "Record context switch events"),
        OPT_BOOLEAN_FLAG(0, "all-kernel", &record.opts.all_kernel,
                         "Configure all used events to run in kernel space.",
                         PARSE_OPT_EXCLUSIVE),

diff --git a/tools/perf/util/record.h b/tools/perf/util/record.h
index 923565c..39d1de4 100644 (file)
--- a/tools/perf/util/record.h
+++ b/tools/perf/util/record.h
@@ -36,6 +36,7 @@ struct record_opts {
        bool          record_namespaces;
        bool          record_cgroup;
        bool          record_switch_events;
+       bool          record_switch_events_set;
        bool          all_kernel;
        bool          all_user;
        bool          kernel_callchains;
@@ -76,4 +77,9 @@ extern struct option *record_options;
 
 int record__parse_freq(const struct option *opt, const char *str, int unset);
 
+static inline bool record_opts__no_switch_events(const struct record_opts *opts)
+{
+       return opts->record_switch_events_set && !opts->record_switch_events;
+}
+
 #endif // _PERF_RECORD_H