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The perf tool has previously made legacy events the priority so with
or without a PMU the legacy event would be opened:
$ perf stat -e cpu-cycles,cpu/cpu-cycles/ true
Using CPUID GenuineIntel-6-8D-1
intel_pt default config: tsc,mtc,mtc_period=3,psb_period=3,pt,branch
Attempting to add event pmu 'cpu' with 'cpu-cycles,' that may result in non-fatal errors
After aliases, add event pmu 'cpu' with 'cpu-cycles,' that may result in non-fatal errors
Control descriptor is not initialized
------------------------------------------------------------
perf_event_attr:
type 0 (PERF_TYPE_HARDWARE)
size 136
config 0 (PERF_COUNT_HW_CPU_CYCLES)
sample_type IDENTIFIER
read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
disabled 1
inherit 1
enable_on_exec 1
exclude_guest 1
------------------------------------------------------------
sys_perf_event_open: pid 833967 cpu -1 group_fd -1 flags 0x8 = 3
------------------------------------------------------------
perf_event_attr:
type 0 (PERF_TYPE_HARDWARE)
size 136
config 0 (PERF_COUNT_HW_CPU_CYCLES)
sample_type IDENTIFIER
read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
disabled 1
inherit 1
enable_on_exec 1
exclude_guest 1
------------------------------------------------------------
...
Fixes to make hybrid/BIG.little PMUs behave correctly, ie as core PMUs
capable of opening legacy events on each, removing hard coded
"cpu_core" and "cpu_atom" Intel PMU names, etc. caused a behavioral
difference on Apple/ARM due to latent issues in the PMU driver
reported in:
https://lore.kernel.org/lkml/08f1f185-e259-4014-9ca4-6411d5c1bc65@marcan.st/
As part of that report Mark Rutland mark.rutland@arm.com requested
that legacy events not be higher in priority when a PMU is specified
reversing what has until this change been perf's default
behavior. With this change the above becomes:
$ perf stat -e cpu-cycles,cpu/cpu-cycles/ true
Using CPUID GenuineIntel-6-8D-1
Attempt to add: cpu/cpu-cycles=0/
..after resolving event: cpu/event=0x3c/
Control descriptor is not initialized
------------------------------------------------------------
perf_event_attr:
type 0 (PERF_TYPE_HARDWARE)
size 136
config 0 (PERF_COUNT_HW_CPU_CYCLES)
sample_type IDENTIFIER
read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
disabled 1
inherit 1
enable_on_exec 1
exclude_guest 1
------------------------------------------------------------
sys_perf_event_open: pid 827628 cpu -1 group_fd -1 flags 0x8 = 3
------------------------------------------------------------
perf_event_attr:
type 4 (PERF_TYPE_RAW)
size 136
config 0x3c
sample_type IDENTIFIER
read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
disabled 1
inherit 1
enable_on_exec 1
exclude_guest 1
------------------------------------------------------------
...
So the second event has become a raw event as
/sys/devices/cpu/events/cpu-cycles exists.
A fix was necessary to config_term_pmu in parse-events.c as
check_alias expansion needs to happen after config_term_pmu, and
config_term_pmu may need calling a second time because of this.
config_term_pmu is updated to not use the legacy event when the PMU
has such a named event (either from json or sysfs).
The bulk of this change is updating all of the parse-events test
expectations so that if a sysfs/json event exists for a PMU the test
doesn't fail - a further sign, if it were needed, that the legacy
event priority was a known and tested behavior of the perf tool.
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