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perf intel-pt: Do not default to recording all switch events

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On systems with many CPUs, recording extra context switch events can be
excessive and unnecessary. Add perf config intel-pt.all-switch-events=false
to control the behaviour.

Example:

 # perf config intel-pt.all-switch-events=false
 # perf record -eintel_pt//u uname
 Linux
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 0.082 MB perf.data ]
 # perf script -D | grep PERF_RECORD_SWITCH | awk '{print $5}' | uniq -c
       5 PERF_RECORD_SWITCH
 # perf config intel-pt.all-switch-events=true
 # perf record -eintel_pt//u uname
 Linux
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 0.102 MB perf.data ]
 # perf script -D | grep PERF_RECORD_SWITCH | awk '{print $5}' | uniq -c
     180 PERF_RECORD_SWITCH_CPU_WIDE

Committer testing:

While doing a make -j28 allmodconfig:

  root@five:~# grep "model name" -m1 /proc/cpuinfo
  model name	: Intel(R) Core(TM) i7-14700K
  root@five:~#
  root@five:~# perf config intel-pt.all-switch-events=false
  root@five:~# perf record -e intel_pt//u uname
  Linux
  [ perf record: Woken up 2 times to write data ]
  [ perf record: Captured and wrote 0.019 MB perf.data ]
  root@five:~# perf report --stats | grep SWITCH_CPU_WIDE
  root@five:~#
  root@five:~# perf config intel-pt.all-switch-events=true
  root@five:~# perf record -e intel_pt//u uname
  Linux
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.047 MB perf.data ]
  root@five:~# perf report --stats | grep SWITCH_CPU_WIDE
       SWITCH_CPU_WIDE events:        542  (96.4%)
  root@five:~#

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20250512093932.79854-3-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Adrian Hunter 2025-05-12 12:39:31 +03:00 committed by Arnaldo Carvalho de Melo
parent e00eac6b5b
commit 352b088164
2 changed files with 19 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
tools/perf/Documentation/perf-config.txt
View File

@ -708,6 +708,10 @@ intel-pt.*::
the maximum is exceeded there will be a "Never-ending loop"
error. The default is 100000.
intel-pt.all-switch-events::
If the user has permission to do so, always record all context
switch events on all CPUs.
auxtrace.*::
auxtrace.dumpdir::

16
tools/perf/arch/x86/util/intel-pt.c
View File

@ -19,6 +19,7 @@
#include "../../../util/evlist.h"
#include "../../../util/evsel.h"
#include "../../../util/evsel_config.h"
#include "../../../util/config.h"
#include "../../../util/cpumap.h"
#include "../../../util/mmap.h"
#include <subcmd/parse-options.h>
@ -52,6 +53,7 @@ struct intel_pt_recording {
struct perf_pmu *intel_pt_pmu;
int have_sched_switch;
struct evlist *evlist;
bool all_switch_events;
bool snapshot_mode;
bool snapshot_init_done;
size_t snapshot_size;
@ -794,7 +796,7 @@ static int intel_pt_recording_options(struct auxtrace_record *itr,
bool cpu_wide = !target__none(&opts->target) &&
!target__has_task(&opts->target);
if (!cpu_wide && perf_can_record_cpu_wide()) {
if (ptr->all_switch_events && !cpu_wide && perf_can_record_cpu_wide()) {
struct evsel *switch_evsel;
switch_evsel = evlist__add_dummy_on_all_cpus(evlist);
@ -1178,6 +1180,16 @@ static u64 intel_pt_reference(struct auxtrace_record *itr __maybe_unused)
return rdtsc();
}
static int intel_pt_perf_config(const char *var, const char *value, void *data)
{
struct intel_pt_recording *ptr = data;
if (!strcmp(var, "intel-pt.all-switch-events"))
ptr->all_switch_events = perf_config_bool(var, value);
return 0;
}
struct auxtrace_record *intel_pt_recording_init(int *err)
{
struct perf_pmu *intel_pt_pmu = perf_pmus__find(INTEL_PT_PMU_NAME);
@ -1197,6 +1209,8 @@ struct auxtrace_record *intel_pt_recording_init(int *err)
return NULL;
}
perf_config(intel_pt_perf_config, ptr);
ptr->intel_pt_pmu = intel_pt_pmu;
ptr->itr.recording_options = intel_pt_recording_options;
ptr->itr.info_priv_size = intel_pt_info_priv_size;