On Tue, Sep 12, 2023 at 03:44:32PM +0300, Tero Kristo wrote:
> Per-package perf events are typically registered with a single CPU only,
> however they can be read across all the CPUs within the package.
> Currently perf_event_read maps the event CPU according to the topology
> information to avoid an unnecessary SMP call, however
> perf_event_read_local deals with hard values and rejects a read with a
> failure if the CPU is not the one exactly registered. Allow similar
> mapping within the perf_event_read_local if the perf event in question
> can support this.
>
> This allows users like BPF code to read the package perf events properly
> across different CPUs within a package.
>
> Signed-off-by: Tero Kristo <tero.kristo@xxxxxxxxxxxxxxx>
> ---
> kernel/events/core.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 4c72a41f11af..780dde646e8a 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4528,6 +4528,7 @@ int perf_event_read_local(struct perf_event *event, u64 *value,
> {
> unsigned long flags;
> int ret = 0;
> + int event_cpu;
>
> /*
> * Disabling interrupts avoids all counter scheduling (context
> @@ -4551,15 +4552,18 @@ int perf_event_read_local(struct perf_event *event, u64 *value,
> goto out;
> }
>
> + event_cpu = READ_ONCE(event->oncpu);
> + event_cpu = __perf_event_read_cpu(event, event_cpu);
What happens with __perf_event_read_cpu() when event_cpu == -1 ?
> +
> /* If this is a per-CPU event, it must be for this CPU */
> if (!(event->attach_state & PERF_ATTACH_TASK) &&
> - event->cpu != smp_processor_id()) {
> + event_cpu != smp_processor_id()) {
> ret = -EINVAL;
> goto out;
> }
>
> /* If this is a pinned event it must be running on this CPU */
> - if (event->attr.pinned && event->oncpu != smp_processor_id()) {
> + if (event->attr.pinned && event_cpu != smp_processor_id()) {
> ret = -EBUSY;
> goto out;
> }
> @@ -4569,7 +4573,7 @@ int perf_event_read_local(struct perf_event *event, u64 *value,
> * or local to this CPU. Furthermore it means its ACTIVE (otherwise
> * oncpu == -1).
> */
> - if (event->oncpu == smp_processor_id())
> + if (event_cpu == smp_processor_id())
> event->pmu->read(event);
>
> *value = local64_read(&event->count);
> --
> 2.40.1
>
