Messages in this thread | | | From | Vince Weaver <> | Date | Wed, 15 Jun 2022 13:57:03 -0400 (EDT) | Subject | [perf] why is /proc/sys/kernel/perf_user_access ARM64 only? |
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Just wasted a lot of time tracking down why rdpmc() event reading wasn't working on an ARM64 machine.
It turns out ARM64 has added a custom "/proc/sys/kernel/perf_user_access" to control rdpmc access, but only on ARM64. e2012600810c9ded81f6f63a8d04781be3c300ad
Why is this ARM64-only? Why isn't this generic perf infrastructure? How is this different from the existing /sys/bus/event_source/devices/cpu/rdpmc tooling?
Also, when user events are disabled, why is the ARMv8 PMU not disabling the cap_user_rdpmc bit in the perf mmap() page?
rdpmc was trouble before, but now it's an even bigger architecture-dependent mess just trying to figure out if the feature is enabled or not.
Vince
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