User space tasks can migrate between CPUs, track sideband events for all
CPUs.
The specific scenarios are as follows:
CPU0 CPU1
perf record -C 0 start
taskA starts to be created and executed
-> PERF_RECORD_COMM and PERF_RECORD_MMAP
events only deliver to CPU1
......
|
migrate to CPU0
|
Running on CPU0 <----------/
...
perf record -C 0 stop
Now perf samples the PC of taskA. However, perf does not record the
PERF_RECORD_COMM and PERF_RECORD_COMM events of taskA.
Therefore, the comm and symbols of taskA cannot be parsed.
The sys_perf_event_open invoked is as follows:
# perf --debug verbose=3 record -e cpu-clock -C 1 true
<SNIP>
Opening: cpu-clock
------------------------------------------------------------
perf_event_attr:
type 1
size 136
{ sample_period, sample_freq } 4000
sample_type IP|TID|TIME|ID|CPU|PERIOD
read_format ID|LOST
disabled 1
inherit 1
freq 1
sample_id_all 1
exclude_guest 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 5
Opening: dummy:HG
------------------------------------------------------------
perf_event_attr:
type 1
size 136
config 0x9
{ sample_period, sample_freq } 1
sample_type IP|TID|TIME|CPU|IDENTIFIER
read_format ID|LOST
inherit 1
exclude_kernel 1
exclude_hv 1
mmap 1
comm 1
task 1
sample_id_all 1
exclude_guest 1
mmap2 1
comm_exec 1
ksymbol 1
bpf_event 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 6
sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 7
sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8 = 9
sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8 = 10
sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8 = 11
sys_perf_event_open: pid -1 cpu 5 group_fd -1 flags 0x8 = 12
sys_perf_event_open: pid -1 cpu 6 group_fd -1 flags 0x8 = 13
sys_perf_event_open: pid -1 cpu 7 group_fd -1 flags 0x8 = 14
<SNIP>
Changes since v1:
- Add perf_evlist__go_system_wide() via internal/evlist.h instead of
exporting perf_evlist__propagate_maps().
- Use evlist__add_aux_dummy() instead of evlist__add_dummy() in
evlist__findnew_tracking_event().
- Add a parameter in evlist__findnew_tracking_event() to deal with
system_wide inside.
- Add sideband for all CPUs when tracing selected CPUs comments on
the perf record man page.
- Use "sideband events" instead of "tracking events".
- Adjust the patches Sequence.
- Add patch5 to skip dummy event sample_type check for evlist_config.
- Add patch6 to update system-wide-dummy attr values for perf test.
Yang Jihong (7):
perf evlist: Add perf_evlist__go_system_wide() helper
perf evlist: Add evlist__findnew_tracking_event() helper
perf record: Move setting dummy tracking before
record__init_thread_masks()
perf record: Track sideband events for all CPUs when tracing selected
CPUs
perf evlist: Skip dummy event sample_type check for evlist_config
perf test: Update system-wide-dummy attr expected values
perf test: Add test case for record sideband events
tools/lib/perf/evlist.c | 9 +++
tools/lib/perf/include/internal/evlist.h | 2 +
tools/perf/Documentation/perf-record.txt | 3 +
tools/perf/builtin-record.c | 69 ++++++++++++++---------
tools/perf/tests/attr/system-wide-dummy | 12 ++--
tools/perf/tests/shell/record_tracking.sh | 44 +++++++++++++++
tools/perf/util/evlist.c | 18 ++++++
tools/perf/util/evlist.h | 1 +
tools/perf/util/record.c | 7 +++
9 files changed, 132 insertions(+), 33 deletions(-)
create mode 100755 tools/perf/tests/shell/record_tracking.sh
--
2.30.GIT
When dummy tracking go system wide, the mmap cpu mask is changed.
Therefore, needs to be placed before record__init_thread_masks().
Dummy tracking has been set in record__open(), move it before
record__init_thread_masks() and add a helper for unified processing.
The sys_perf_event_open invoked is as follows:
# perf --debug verbose=3 record -e cpu-clock -D 100 true
<SNIP>
Opening: cpu-clock
------------------------------------------------------------
perf_event_attr:
type 1
size 136
{ sample_period, sample_freq } 4000
sample_type IP|TID|TIME|PERIOD|IDENTIFIER
read_format ID|LOST
disabled 1
inherit 1
freq 1
sample_id_all 1
exclude_guest 1
------------------------------------------------------------
sys_perf_event_open: pid 6867 cpu 0 group_fd -1 flags 0x8 = 5
sys_perf_event_open: pid 6867 cpu 1 group_fd -1 flags 0x8 = 6
sys_perf_event_open: pid 6867 cpu 2 group_fd -1 flags 0x8 = 7
sys_perf_event_open: pid 6867 cpu 3 group_fd -1 flags 0x8 = 9
sys_perf_event_open: pid 6867 cpu 4 group_fd -1 flags 0x8 = 10
sys_perf_event_open: pid 6867 cpu 5 group_fd -1 flags 0x8 = 11
sys_perf_event_open: pid 6867 cpu 6 group_fd -1 flags 0x8 = 12
sys_perf_event_open: pid 6867 cpu 7 group_fd -1 flags 0x8 = 13
Opening: dummy:u
------------------------------------------------------------
perf_event_attr:
type 1
size 136
config 0x9
{ sample_period, sample_freq } 1
sample_type IP|TID|TIME|IDENTIFIER
read_format ID|LOST
disabled 1
inherit 1
exclude_kernel 1
exclude_hv 1
mmap 1
comm 1
enable_on_exec 1
task 1
sample_id_all 1
exclude_guest 1
mmap2 1
comm_exec 1
ksymbol 1
bpf_event 1
------------------------------------------------------------
sys_perf_event_open: pid 6867 cpu 0 group_fd -1 flags 0x8 = 14
sys_perf_event_open: pid 6867 cpu 1 group_fd -1 flags 0x8 = 15
sys_perf_event_open: pid 6867 cpu 2 group_fd -1 flags 0x8 = 16
sys_perf_event_open: pid 6867 cpu 3 group_fd -1 flags 0x8 = 17
sys_perf_event_open: pid 6867 cpu 4 group_fd -1 flags 0x8 = 18
sys_perf_event_open: pid 6867 cpu 5 group_fd -1 flags 0x8 = 19
sys_perf_event_open: pid 6867 cpu 6 group_fd -1 flags 0x8 = 20
sys_perf_event_open: pid 6867 cpu 7 group_fd -1 flags 0x8 = 21
<SNIP>
Signed-off-by: Yang Jihong <[email protected]>
---
tools/perf/builtin-record.c | 59 +++++++++++++++++++++++--------------
1 file changed, 37 insertions(+), 22 deletions(-)
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index ca83599cc50c..ccbcb005e188 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -908,6 +908,37 @@ static int record__config_off_cpu(struct record *rec)
return off_cpu_prepare(rec->evlist, &rec->opts.target, &rec->opts);
}
+static int record__config_tracking_events(struct record *rec)
+{
+ struct evsel *evsel;
+ struct evlist *evlist = rec->evlist;
+ struct record_opts *opts = &rec->opts;
+
+ /*
+ * For initial_delay, system wide or a hybrid system, we need to add a
+ * dummy event so that we can track PERF_RECORD_MMAP to cover the delay
+ * of waiting or event synthesis.
+ */
+ if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
+ perf_pmus__num_core_pmus() > 1) {
+ evsel = evlist__findnew_tracking_event(evlist, false);
+ if (!evsel)
+ return -ENOMEM;
+
+ /*
+ * Enable the dummy event when the process is forked for
+ * initial_delay, immediately for system wide.
+ */
+ if (opts->target.initial_delay && !evsel->immediate &&
+ !target__has_cpu(&opts->target))
+ evsel->core.attr.enable_on_exec = 1;
+ else
+ evsel->immediate = 1;
+ }
+
+ return 0;
+}
+
static bool record__kcore_readable(struct machine *machine)
{
char kcore[PATH_MAX];
@@ -1288,28 +1319,6 @@ static int record__open(struct record *rec)
struct record_opts *opts = &rec->opts;
int rc = 0;
- /*
- * For initial_delay, system wide or a hybrid system, we need to add a
- * dummy event so that we can track PERF_RECORD_MMAP to cover the delay
- * of waiting or event synthesis.
- */
- if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
- perf_pmus__num_core_pmus() > 1) {
- pos = evlist__findnew_tracking_event(evlist, false);
- if (!pos)
- return -ENOMEM;
-
- /*
- * Enable the dummy event when the process is forked for
- * initial_delay, immediately for system wide.
- */
- if (opts->target.initial_delay && !pos->immediate &&
- !target__has_cpu(&opts->target))
- pos->core.attr.enable_on_exec = 1;
- else
- pos->immediate = 1;
- }
-
evlist__config(evlist, opts, &callchain_param);
evlist__for_each_entry(evlist, pos) {
@@ -4235,6 +4244,12 @@ int cmd_record(int argc, const char **argv)
goto out;
}
+ err = record__config_tracking_events(rec);
+ if (err) {
+ pr_err("record__config_tracking_events failed, error %d\n", err);
+ goto out;
+ }
+
err = record__init_thread_masks(rec);
if (err) {
pr_err("Failed to initialize parallel data streaming masks\n");
--
2.30.GIT
The perf record uses evlist__add_aux_dummy() instead of evlist__add_dummy()
to add a dummy event. The value of attr needs to be updated.
The perf test result is as follows:
# ./perf test list 2>&1 | grep 'Setup struct perf_event_attr'
17: Setup struct perf_event_attr
# ./perf test 17
17: Setup struct perf_event_attr : Ok
Signed-off-by: Yang Jihong <[email protected]>
---
tools/perf/tests/attr/system-wide-dummy | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/tools/perf/tests/attr/system-wide-dummy b/tools/perf/tests/attr/system-wide-dummy
index 2f3e3eb728eb..69f61f3271cc 100644
--- a/tools/perf/tests/attr/system-wide-dummy
+++ b/tools/perf/tests/attr/system-wide-dummy
@@ -9,8 +9,8 @@ flags=8
type=1
size=136
config=9
-sample_period=4000
-sample_type=455
+sample_period=1
+sample_type=199
read_format=4|20
# Event will be enabled right away.
disabled=0
@@ -18,12 +18,12 @@ inherit=1
pinned=0
exclusive=0
exclude_user=0
-exclude_kernel=0
-exclude_hv=0
+exclude_kernel=1
+exclude_hv=1
exclude_idle=0
mmap=1
comm=1
-freq=1
+freq=0
inherit_stat=0
enable_on_exec=0
task=1
@@ -32,7 +32,7 @@ precise_ip=0
mmap_data=0
sample_id_all=1
exclude_host=0
-exclude_guest=0
+exclude_guest=1
exclude_callchain_kernel=0
exclude_callchain_user=0
mmap2=1
--
2.30.GIT
User space tasks can migrate between CPUs, we need to track side-band
events for all CPUs.
The specific scenarios are as follows:
CPU0 CPU1
perf record -C 0 start
taskA starts to be created and executed
-> PERF_RECORD_COMM and PERF_RECORD_MMAP
events only deliver to CPU1
......
|
migrate to CPU0
|
Running on CPU0 <----------/
...
perf record -C 0 stop
Now perf samples the PC of taskA. However, perf does not record the
PERF_RECORD_COMM and PERF_RECORD_MMAP events of taskA.
Therefore, the comm and symbols of taskA cannot be parsed.
The solution is to record sideband events for all CPUs when tracing
selected CPUs. Because this modifies the default behavior, add related
comments to the perf record man page.
The sys_perf_event_open invoked is as follows:
# perf --debug verbose=3 record -e cpu-clock -C 1 true
<SNIP>
Opening: cpu-clock
------------------------------------------------------------
perf_event_attr:
type 1
size 136
{ sample_period, sample_freq } 4000
sample_type IP|TID|TIME|ID|CPU|PERIOD
read_format ID|LOST
disabled 1
inherit 1
freq 1
sample_id_all 1
exclude_guest 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 5
Opening: dummy:HG
------------------------------------------------------------
perf_event_attr:
type 1
size 136
config 0x9
{ sample_period, sample_freq } 1
sample_type IP|TID|TIME|CPU|IDENTIFIER
read_format ID|LOST
inherit 1
exclude_kernel 1
exclude_hv 1
mmap 1
comm 1
task 1
sample_id_all 1
exclude_guest 1
mmap2 1
comm_exec 1
ksymbol 1
bpf_event 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 6
sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 7
sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8 = 9
sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8 = 10
sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8 = 11
sys_perf_event_open: pid -1 cpu 5 group_fd -1 flags 0x8 = 12
sys_perf_event_open: pid -1 cpu 6 group_fd -1 flags 0x8 = 13
sys_perf_event_open: pid -1 cpu 7 group_fd -1 flags 0x8 = 14
<SNIP>
Signed-off-by: Yang Jihong <[email protected]>
---
tools/perf/Documentation/perf-record.txt | 3 +++
tools/perf/builtin-record.c | 7 ++++++-
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 680396c56bd1..dac53ece51ab 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -388,6 +388,9 @@ comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-
In per-thread mode with inheritance mode on (default), samples are captured only when
the thread executes on the designated CPUs. Default is to monitor all CPUs.
+User space tasks can migrate between CPUs, so when tracing selected CPUs,
+a dummy event is created to track sideband for all CPUs.
+
-B::
--no-buildid::
Do not save the build ids of binaries in the perf.data files. This skips
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index ccbcb005e188..4a15b2e06f45 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -921,7 +921,12 @@ static int record__config_tracking_events(struct record *rec)
*/
if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
perf_pmus__num_core_pmus() > 1) {
- evsel = evlist__findnew_tracking_event(evlist, false);
+
+ /*
+ * User space tasks can migrate between CPUs, so when tracing
+ * selected CPUs, sideband for all CPUs is still needed.
+ */
+ evsel = evlist__findnew_tracking_event(evlist, !!opts->target.cpu_list);
if (!evsel)
return -ENOMEM;
--
2.30.GIT
On 15/07/23 06:29, Yang Jihong wrote:
> User space tasks can migrate between CPUs, we need to track side-band
> events for all CPUs.
>
> The specific scenarios are as follows:
>
> CPU0 CPU1
> perf record -C 0 start
> taskA starts to be created and executed
> -> PERF_RECORD_COMM and PERF_RECORD_MMAP
> events only deliver to CPU1
> ......
> |
> migrate to CPU0
> |
> Running on CPU0 <----------/
> ...
>
> perf record -C 0 stop
>
> Now perf samples the PC of taskA. However, perf does not record the
> PERF_RECORD_COMM and PERF_RECORD_MMAP events of taskA.
> Therefore, the comm and symbols of taskA cannot be parsed.
>
> The solution is to record sideband events for all CPUs when tracing
> selected CPUs. Because this modifies the default behavior, add related
> comments to the perf record man page.
>
> The sys_perf_event_open invoked is as follows:
>
> # perf --debug verbose=3 record -e cpu-clock -C 1 true
> <SNIP>
> Opening: cpu-clock
> ------------------------------------------------------------
> perf_event_attr:
> type 1
> size 136
> { sample_period, sample_freq } 4000
> sample_type IP|TID|TIME|ID|CPU|PERIOD
> read_format ID|LOST
> disabled 1
> inherit 1
> freq 1
> sample_id_all 1
> exclude_guest 1
> ------------------------------------------------------------
> sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 5
> Opening: dummy:HG
> ------------------------------------------------------------
> perf_event_attr:
> type 1
> size 136
> config 0x9
> { sample_period, sample_freq } 1
> sample_type IP|TID|TIME|CPU|IDENTIFIER
> read_format ID|LOST
> inherit 1
> exclude_kernel 1
> exclude_hv 1
> mmap 1
> comm 1
> task 1
> sample_id_all 1
> exclude_guest 1
> mmap2 1
> comm_exec 1
> ksymbol 1
> bpf_event 1
> ------------------------------------------------------------
> sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 6
> sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 7
> sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8 = 9
> sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8 = 10
> sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8 = 11
> sys_perf_event_open: pid -1 cpu 5 group_fd -1 flags 0x8 = 12
> sys_perf_event_open: pid -1 cpu 6 group_fd -1 flags 0x8 = 13
> sys_perf_event_open: pid -1 cpu 7 group_fd -1 flags 0x8 = 14
> <SNIP>
>
> Signed-off-by: Yang Jihong <[email protected]>
> ---
> tools/perf/Documentation/perf-record.txt | 3 +++
> tools/perf/builtin-record.c | 7 ++++++-
> 2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
> index 680396c56bd1..dac53ece51ab 100644
> --- a/tools/perf/Documentation/perf-record.txt
> +++ b/tools/perf/Documentation/perf-record.txt
> @@ -388,6 +388,9 @@ comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-
> In per-thread mode with inheritance mode on (default), samples are captured only when
> the thread executes on the designated CPUs. Default is to monitor all CPUs.
>
> +User space tasks can migrate between CPUs, so when tracing selected CPUs,
> +a dummy event is created to track sideband for all CPUs.
> +
> -B::
> --no-buildid::
> Do not save the build ids of binaries in the perf.data files. This skips
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index ccbcb005e188..4a15b2e06f45 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -921,7 +921,12 @@ static int record__config_tracking_events(struct record *rec)
> */
> if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
> perf_pmus__num_core_pmus() > 1) {
> - evsel = evlist__findnew_tracking_event(evlist, false);
> +
> + /*
> + * User space tasks can migrate between CPUs, so when tracing
> + * selected CPUs, sideband for all CPUs is still needed.
So if all (non-dummy) evsel have exclude_user, then system_wide is not needed.
> + */
> + evsel = evlist__findnew_tracking_event(evlist, !!opts->target.cpu_list);
> if (!evsel)
> return -ENOMEM;
>
Hello,
On 2023/7/17 22:25, Adrian Hunter wrote:
> On 15/07/23 06:29, Yang Jihong wrote:
>> User space tasks can migrate between CPUs, we need to track side-band
>> events for all CPUs.
>>
>> The specific scenarios are as follows:
>>
>> CPU0 CPU1
>> perf record -C 0 start
>> taskA starts to be created and executed
>> -> PERF_RECORD_COMM and PERF_RECORD_MMAP
>> events only deliver to CPU1
>> ......
>> |
>> migrate to CPU0
>> |
>> Running on CPU0 <----------/
>> ...
>>
>> perf record -C 0 stop
>>
>> Now perf samples the PC of taskA. However, perf does not record the
>> PERF_RECORD_COMM and PERF_RECORD_MMAP events of taskA.
>> Therefore, the comm and symbols of taskA cannot be parsed.
>>
>> The solution is to record sideband events for all CPUs when tracing
>> selected CPUs. Because this modifies the default behavior, add related
>> comments to the perf record man page.
>>
>> The sys_perf_event_open invoked is as follows:
>>
>> # perf --debug verbose=3 record -e cpu-clock -C 1 true
>> <SNIP>
>> Opening: cpu-clock
>> ------------------------------------------------------------
>> perf_event_attr:
>> type 1
>> size 136
>> { sample_period, sample_freq } 4000
>> sample_type IP|TID|TIME|ID|CPU|PERIOD
>> read_format ID|LOST
>> disabled 1
>> inherit 1
>> freq 1
>> sample_id_all 1
>> exclude_guest 1
>> ------------------------------------------------------------
>> sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 5
>> Opening: dummy:HG
>> ------------------------------------------------------------
>> perf_event_attr:
>> type 1
>> size 136
>> config 0x9
>> { sample_period, sample_freq } 1
>> sample_type IP|TID|TIME|CPU|IDENTIFIER
>> read_format ID|LOST
>> inherit 1
>> exclude_kernel 1
>> exclude_hv 1
>> mmap 1
>> comm 1
>> task 1
>> sample_id_all 1
>> exclude_guest 1
>> mmap2 1
>> comm_exec 1
>> ksymbol 1
>> bpf_event 1
>> ------------------------------------------------------------
>> sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 6
>> sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 7
>> sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8 = 9
>> sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8 = 10
>> sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8 = 11
>> sys_perf_event_open: pid -1 cpu 5 group_fd -1 flags 0x8 = 12
>> sys_perf_event_open: pid -1 cpu 6 group_fd -1 flags 0x8 = 13
>> sys_perf_event_open: pid -1 cpu 7 group_fd -1 flags 0x8 = 14
>> <SNIP>
>>
>> Signed-off-by: Yang Jihong <[email protected]>
>> ---
>> tools/perf/Documentation/perf-record.txt | 3 +++
>> tools/perf/builtin-record.c | 7 ++++++-
>> 2 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
>> index 680396c56bd1..dac53ece51ab 100644
>> --- a/tools/perf/Documentation/perf-record.txt
>> +++ b/tools/perf/Documentation/perf-record.txt
>> @@ -388,6 +388,9 @@ comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-
>> In per-thread mode with inheritance mode on (default), samples are captured only when
>> the thread executes on the designated CPUs. Default is to monitor all CPUs.
>>
>> +User space tasks can migrate between CPUs, so when tracing selected CPUs,
>> +a dummy event is created to track sideband for all CPUs.
>> +
>> -B::
>> --no-buildid::
>> Do not save the build ids of binaries in the perf.data files. This skips
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index ccbcb005e188..4a15b2e06f45 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -921,7 +921,12 @@ static int record__config_tracking_events(struct record *rec)
>> */
>> if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
>> perf_pmus__num_core_pmus() > 1) {
>> - evsel = evlist__findnew_tracking_event(evlist, false);
>> +
>> + /*
>> + * User space tasks can migrate between CPUs, so when tracing
>> + * selected CPUs, sideband for all CPUs is still needed.
>
> So if all (non-dummy) evsel have exclude_user, then system_wide is not needed.
OK, The previous judgment system_wide is simplified and will be refined
here.
>
>> + */
>> + evsel = evlist__findnew_tracking_event(evlist, !!opts->target.cpu_list);
>> if (!evsel)
>> return -ENOMEM;
>>
>
> .
>