• Mark Rutland's avatar
    arm_pmu: fix event CPU filtering · 61d03862
    Mark Rutland authored
    Janne reports that perf has been broken on Apple M1 as of commit:
    
      bd275681 ("perf: Rewrite core context handling")
    
    That commit replaced the pmu::filter_match() callback with
    pmu::filter(), whose return value has the opposite polarity, with true
    implying events should be ignored rather than scheduled. While an
    attempt was made to update the logic in armv8pmu_filter() and
    armpmu_filter() accordingly, the return value remains inverted in a
    couple of cases:
    
    * If the arm_pmu does not have an arm_pmu::filter() callback,
      armpmu_filter() will always return whether the CPU is supported rather
      than whether the CPU is not supported.
    
      As a result, the perf core will not schedule events on supported CPUs,
      resulting in a loss of events. Additionally, the perf core will
      attempt to schedule events on unsupported CPUs, but this will be
      rejected by armpmu_add(), which may result in a loss of events from
      other PMUs on those unsupported CPUs.
    
    * If the arm_pmu does have an arm_pmu::filter() callback, and
      armpmu_filter() is called on a CPU which is not supported by the
      arm_pmu, armpmu_filter() will return false rather than true.
    
      As a result, the perf core will attempt to schedule events on
      unsupported CPUs, but this will be rejected by armpmu_add(), which may
      result in a loss of events from other PMUs on those unsupported CPUs.
    
    This means a loss of events can be seen with any arm_pmu driver, but
    with the ARMv8 PMUv3 driver (which is the only arm_pmu driver with an
    arm_pmu::filter() callback) the event loss will be more limited and may
    go unnoticed, which is how this issue evaded testing so far.
    
    Fix the CPU filtering by performing this consistently in
    armpmu_filter(), and remove the redundant arm_pmu::filter() callback and
    armv8pmu_filter() implementation.
    
    Commit bd275681 also silently removed the CHAIN event filtering from
    armv8pmu_filter(), which will be addressed by a separate patch without
    using the filter callback.
    
    Fixes: bd275681 ("perf: Rewrite core context handling")
    Reported-by: default avatarJanne Grunau <j@jannau.net>
    Link: https://lore.kernel.org/asahi/20230215-arm_pmu_m1_regression-v1-1-f5a266577c8d@jannau.net/Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
    Cc: Will Deacon <will@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Ravi Bangoria <ravi.bangoria@amd.com>
    Cc: Asahi Lina <lina@asahilina.net>
    Cc: Eric Curtin <ecurtin@redhat.com>
    Tested-by: default avatarJanne Grunau <j@jannau.net>
    Link: https://lore.kernel.org/r/20230216141240.3833272-2-mark.rutland@arm.comSigned-off-by: default avatarWill Deacon <will@kernel.org>
    61d03862
arm_pmu.c 22.6 KB