perf: arm_pmuv3: Don't use PMCCNTR_EL0 on SMT cores

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CPU_CYCLES is expected to count the logical CPU (PE) clock. Currently it's
preferred to use PMCCNTR_EL0 for counting CPU_CYCLES, but it'll count
processor clock rather than the PE clock (ARM DDI0487 L.b D13.1.3) if
one of the SMT siblings is not idle on a multi-threaded implementation.
So don't use it on SMT cores.

Introduce topology_core_has_smt() for knowing the SMT implementation and
cached it in arm_pmu::has_smt during allocation.

When counting cycles on SMT CPU 2-3 and CPU 3 is idle, without this
patch we'll get:
[root@client1 tmp]# perf stat -e cycles -A -C 2-3 -- stress-ng -c 1
--taskset 2 --timeout 1
[...]
 Performance counter stats for 'CPU(s) 2-3':

CPU2           2880457316      cycles
CPU3           2880459810      cycles
       1.254688470 seconds time elapsed

With this patch the idle state of CPU3 is observed as expected:
[root@client1 ~]#  perf stat -e cycles -A -C 2-3 -- stress-ng -c 1
--taskset 2 --timeout 1
[...]
 Performance counter stats for 'CPU(s) 2-3':

CPU2           2558580492      cycles
CPU3               305749      cycles
       1.113626410 seconds time elapsed

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Will Deacon <will@kernel.org>

...

This commit is contained in:

Yicong Yang 2025-09-22 11:30:10 +08:00 • committed by Will Deacon

parent 3a86608788

commit c3d78c34ad

4 changed files with 28 additions and 0 deletions

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6

drivers/perf/arm_pmu.c

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10

drivers/perf/arm_pmuv3.c

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11

include/linux/arch_topology.h

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1

include/linux/perf/arm_pmu.h

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