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    SubjectRe: [PATCH 1/3] perf/core: Flush PMU internal buffers for per-CPU events
    On Mon, Nov 09, 2020 at 09:49:31AM -0500, Liang, Kan wrote:
    > > Maybe we can frob x86_pmu_enable()...
    >
    > Could you please elaborate?

    Something horrible like this. It will detect the first time we enable
    the PMU on a new task (IOW we did a context switch) and wipe the
    counters when user RDPMC is on...

    diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
    index 77b963e5e70a..d862927baaef 100644
    --- a/arch/x86/events/core.c
    +++ b/arch/x86/events/core.c
    @@ -1289,6 +1289,15 @@ static void x86_pmu_enable(struct pmu *pmu)
    perf_events_lapic_init();
    }

    + if (cpuc->current != current) {
    + struct mm_struct *mm = current->mm;
    +
    + cpuc->current = current;
    +
    + if (mm && atomic_read(&mm->context.perf_rdpmc_allowed))
    + wipe_dirty_counters();
    + }
    +
    cpuc->enabled = 1;
    barrier();

    diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
    index 7895cf4c59a7..d16118cb3bd0 100644
    --- a/arch/x86/events/perf_event.h
    +++ b/arch/x86/events/perf_event.h
    @@ -248,6 +248,8 @@ struct cpu_hw_events {
    unsigned int txn_flags;
    int is_fake;

    + void *current;
    +
    /*
    * Intel DebugStore bits
    */
    \
     
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      Last update: 2020-11-09 18:33    [W:4.189 / U:0.060 seconds]
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