[PATCH v3 27/27] perf Documentation: Document intel-hybrid support

Jin Yao
2021-03-29T07:03:47Z

Add some words and examples to help understanding of
Intel hybrid perf support.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
---
v3:
- No functional change.

tools/perf/Documentation/intel-hybrid.txt | 228 ++++++++++++++++++++++
tools/perf/Documentation/perf-record.txt | 1 +
tools/perf/Documentation/perf-stat.txt | 2 +
3 files changed, 231 insertions(+)
create mode 100644 tools/perf/Documentation/intel-hybrid.txt

diff --git a/tools/perf/Documentation/intel-hybrid.txt b/tools/perf/Documentation/intel-hybrid.txt
new file mode 100644
index 000000000000..784f598dd36f
--- /dev/null
+++ b/tools/perf/Documentation/intel-hybrid.txt
@@ -0,0 +1,228 @@
+Intel hybrid support
+--------------------
+Support for Intel hybrid events within perf tools.
+
+For some Intel platforms, such as AlderLake, which is hybrid platform and
+it consists of atom cpu and core cpu. Each cpu has dedicated event list.
+Part of events are available on core cpu, part of events are available
+on atom cpu and even part of events are available on both.
+
+Kernel exports two new cpu pmus via sysfs:
+/sys/devices/cpu_core
+/sys/devices/cpu_atom
+
+The 'cpus' files are created under the directories. For example,
+
+cat /sys/devices/cpu_core/cpus
+0-15
+
+cat /sys/devices/cpu_atom/cpus
+16-23
+
+It indicates cpu0-cpu15 are core cpus and cpu16-cpu23 are atom cpus.
+
+Quickstart
+
+List hybrid event
+-----------------
+
+As before, use perf-list to list the symbolic event.
+
+perf list
+
+inst_retired.any
+ [Fixed Counter: Counts the number of instructions retired. Unit: cpu_atom]
+inst_retired.any
+ [Number of instructions retired. Fixed Counter - architectural event. Unit: cpu_core]
+
+The 'Unit: xxx' is added to brief description to indicate which pmu
+the event is belong to. Same event name but with different pmu can
+be supported.
+
+Enable hybrid event with a specific pmu
+---------------------------------------
+
+To enable a core only event or atom only event, following syntax is supported:
+
+ cpu_core/<event name>/
+or
+ cpu_atom/<event name>/
+
+For example, count the 'cycles' event on core cpus.
+
+ perf stat -e cpu_core/cycles/
+
+Create two events for one hardware event automatically
+------------------------------------------------------
+
+When creating one event and the event is available on both atom and core,
+two events are created automatically. One is for atom, the other is for
+core. Most of hardware events and cache events are available on both
+cpu_core and cpu_atom.
+
+For hardware events, they have pre-defined configs (e.g. 0 for cycles).
+But on hybrid platform, kernel needs to know where the event comes from
+(from atom or from core). The original perf event type PERF_TYPE_HARDWARE
+can't carry pmu information. So a new type PERF_TYPE_HARDWARE_PMU is
+introduced.
+
+The new attr.config layout for PERF_TYPE_HARDWARE_PMU:
+
+0xDD000000AA
+AA: original hardware event ID
+DD: PMU type ID
+
+Cache event is similar. A new type PERF_TYPE_HW_CACHE_PMU is introduced.
+
+The new attr.config layout for PERF_TYPE_HW_CACHE_PMU:
+
+0xDD00CCBBAA
+AA: original hardware cache ID
+BB: original hardware cache op ID
+CC: original hardware cache op result ID
+DD: PMU type ID
+
+PMU type ID is retrieved from sysfs
+
+cat /sys/devices/cpu_atom/type
+10
+
+cat /sys/devices/cpu_core/type
+4
+
+When enabling a hardware event without specified pmu, such as,
+perf stat -e cycles -a (use system-wide in this example), two events
+are created automatically.
+
+ ------------------------------------------------------------
+ perf_event_attr:
+ type 6
+ size 120
+ config 0x400000000
+ sample_type IDENTIFIER
+ read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
+ disabled 1
+ inherit 1
+ exclude_guest 1
+ ------------------------------------------------------------
+
+and
+
+ ------------------------------------------------------------
+ perf_event_attr:
+ type 6
+ size 120
+ config 0xa00000000
+ sample_type IDENTIFIER
+ read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
+ disabled 1
+ inherit 1
+ exclude_guest 1
+ ------------------------------------------------------------
+
+type 6 is PERF_TYPE_HARDWARE_PMU.
+0x4 in 0x400000000 indicates it's cpu_core pmu.
+0xa in 0xa00000000 indicates it's cpu_atom pmu (atom pmu type id is random).
+
+The kernel creates 'cycles' (0x400000000) on cpu0-cpu15 (core cpus),
+and create 'cycles' (0xa00000000) on cpu16-cpu23 (atom cpus).
+
+For perf-stat result, it displays two events:
+
+ Performance counter stats for 'system wide':
+
+ 12,869,720,529 cpu_core/cycles/
+ 6,405,459,328 cpu_atom/cycles/
+
+The first 'cycles' is core event, the second 'cycles' is atom event.
+
+Thread mode example:
+--------------------
+
+perf-stat reports the scaled counts for hybrid event and with a percentage
+displayed. The percentage is the event's running time/enabling time.
+
+One example, 'triad_loop' runs on cpu16 (atom core), while we can see the
+scaled value for core cycles is 160,444,092 and the percentage is 0.47%.
+
+perf stat -e cycles -- taskset -c 16 ./triad_loop
+
+As previous, two events are created.
+
+------------------------------------------------------------
+perf_event_attr:
+ type 6
+ size 120
+ config 0x400000000
+ sample_type IDENTIFIER
+ read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
+ disabled 1
+ inherit 1
+ enable_on_exec 1
+ exclude_guest 1
+------------------------------------------------------------
+
+and
+
+------------------------------------------------------------
+perf_event_attr:
+ type 6
+ size 120
+ config 0xa00000000
+ sample_type IDENTIFIER
+ read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
+ disabled 1
+ inherit 1
+ enable_on_exec 1
+ exclude_guest 1
+------------------------------------------------------------
+
+cycles: 0: 784136 339210144 1013444
+cycles: 0: 601988862 339210144 338196700
+cycles: 262458394 339210144 1013444
+cycles: 603792788 339210144 338196700
+
+ Performance counter stats for 'taskset -c 16 ./triad_loop':
+
+ 262,458,394 cpu_core/cycles/ (0.30%)
+ 603,792,788 cpu_atom/cycles/ (99.70%)
+
+ 0.340467913 seconds time elapsed
+
+perf-record:
+------------
+
+If there is no '-e' specified in perf record, on hybrid platform,
+it creates two default 'cycles' and adds them to event list. One
+is for core, the other is for atom.
+
+perf-stat:
+----------
+
+If there is no '-e' specified in perf stat, on hybrid platform,
+besides of software events, following events are created and
+added to event list in order.
+
+cpu_core/cycles/,
+cpu_atom/cycles/,
+cpu_core/instructions/,
+cpu_atom/instructions/,
+cpu_core/branches/,
+cpu_atom/branches/,
+cpu_core/branch-misses/,
+cpu_atom/branch-misses/
+
+Of course, both perf-stat and perf-record support to enable
+hybrid event with a specific pmu.
+
+e.g.
+perf stat -e cpu_core/cycles/
+perf stat -e cpu_atom/cycles/
+perf stat -e cpu_core/r1a/
+perf stat -e cpu_atom/L1-icache-loads/
+perf stat -e cpu_core/cycles/,cpu_atom/instructions/
+perf stat -e '{cpu_core/cycles/,cpu_core/instructions/}'
+
+But '{cpu_core/cycles/,cpu_atom/instructions/}' will return
+"<not supported>" for 'instructions', because the pmus in
+group are not matched (cpu_core vs. cpu_atom).
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index f3161c9673e9..d71bac847936 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -695,6 +695,7 @@ measurements:
wait -n ${perf_pid}
exit $?

+include::intel-hybrid.txt[]

SEE ALSO
--------
diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt
index 744211fa8c18..13ec4165004b 100644
--- a/tools/perf/Documentation/perf-stat.txt
+++ b/tools/perf/Documentation/perf-stat.txt
@@ -541,6 +541,8 @@ The fields are in this order:

Additional metrics may be printed with all earlier fields being empty.

+include::intel-hybrid.txt[]
+
SEE ALSO
--------
linkperf:perf-top[1], linkperf:perf-list[1]
--
2.17.1