From: Thomas Richter <tmricht@linux.ibm.com>
To: "linux-perf-use." <linux-perf-users@vger.kernel.org>,
Ian Rogers <irogers@google.com>
Subject: perf record question regarding grouped events
Date: Wed, 19 Feb 2025 11:57:46 +0100 [thread overview]
Message-ID: <e2c7e654-5608-4206-ab3a-2a63b54cbc35@linux.ibm.com> (raw)
Hi all,
I have a question on the intended usage of the grouped events as
in test case 114 perf record tests subtest 'Basic leader sampling' test
where this command is executed:
# perf record -vv -e '{cycles,cycles}:uS' -- ...
In the debug output the following 2 event are installed:
------------------------------------------------------------
perf_event_attr:
type 0 (PERF_TYPE_HARDWARE)
size 136
config 0 (PERF_COUNT_HW_CPU_CYCLES)
{ sample_period, sample_freq } 4000
sample_type IP|TID|TIME|READ|CPU|PERIOD|IDENTIFIER
read_format ID|GROUP|LOST
disabled 1
exclude_kernel 1
exclude_hv 1
freq 1
sample_id_all 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 5
------------------------------------------------------------
perf_event_attr:
type 0 (PERF_TYPE_HARDWARE)
size 136
config 0 (PERF_COUNT_HW_CPU_CYCLES)
sample_type IP|TID|TIME|READ|CPU|PERIOD|IDENTIFIER
read_format ID|GROUP|LOST
exclude_kernel 1
exclude_hv 1
sample_id_all 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 0 group_fd 5 flags 0x8 = 6
What puzzles me is that the first event with file descriptor 5
is installed for sampling. The second event with file descriptor 6
is installed for counting because event attribute members
attr::freq and attr::sample_freq are zero.
So of the 2 cycles events installed, the group leader is sampling
and the other event is counting.
Is this understanding correct?
The test then checks if the number of samples matches the count
from the counting event?
I have a question on the intended usage of the grouped events as
in test case 114 perf record tests subtest 'Basic leader sampling' test
where this command is executed:
# perf record -vv -e '{cycles,cycles}:uS' -- ...
In the debug output the following 2 event are installed:
------------------------------------------------------------
perf_event_attr:
type 0 (PERF_TYPE_HARDWARE)
size 136
config 0 (PERF_COUNT_HW_CPU_CYCLES)
{ sample_period, sample_freq } 4000
sample_type IP|TID|TIME|READ|CPU|PERIOD|IDENTIFIER
read_format ID|GROUP|LOST
disabled 1
exclude_kernel 1
exclude_hv 1
freq 1
sample_id_all 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 5
------------------------------------------------------------
perf_event_attr:
type 0 (PERF_TYPE_HARDWARE)
size 136
config 0 (PERF_COUNT_HW_CPU_CYCLES)
sample_type IP|TID|TIME|READ|CPU|PERIOD|IDENTIFIER
read_format ID|GROUP|LOST
exclude_kernel 1
exclude_hv 1
sample_id_all 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 0 group_fd 5 flags 0x8 = 6
What puzzles me is that the first event with file descriptor 5
is installed for sampling. The second event with file descriptor 6
is installed for counting because event attribute members
attr::freq and attr::sample_freq are zero.
So of the 2 cycles events installed, the group leader is sampling
and the other event is counting.
Is this understanding correct?
The test then checks if the number of samples matches the count
from the counting event?
Thanks a lot for your help.
--
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Wolfgang Wendt
Geschäftsführung: David Faller
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294
next reply other threads:[~2025-02-19 10:57 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-19 10:57 Thomas Richter [this message]
2025-02-24 23:57 ` perf record question regarding grouped events Namhyung Kim
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