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Message-ID: <20240906151153.GX4723@noisy.programming.kicks-ass.net>
Date: Fri, 6 Sep 2024 17:11:53 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: kan.liang@...ux.intel.com
Cc: mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
irogers@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] perf: Add PERF_EV_CAP_READ_SCOPE
On Fri, Aug 02, 2024 at 08:16:38AM -0700, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
>
> Usually, an event can be read from any CPU of the scope. It doesn't need
> to be read from the advertised CPU.
>
> Add a new event cap, PERF_EV_CAP_READ_SCOPE. An event of a PMU with
> scope can be read from any active CPU in the scope.
>
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
> include/linux/perf_event.h | 3 +++
> kernel/events/core.c | 14 +++++++++++---
> 2 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 1102d5c2be70..1206bc86eb4f 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -633,10 +633,13 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *,
> * PERF_EV_CAP_SIBLING: An event with this flag must be a group sibling and
> * cannot be a group leader. If an event with this flag is detached from the
> * group it is scheduled out and moved into an unrecoverable ERROR state.
> + * PERF_EV_CAP_READ_SCOPE: A CPU event that can be read from any CPU of the
> + * PMU scope where it is active.
> */
> #define PERF_EV_CAP_SOFTWARE BIT(0)
> #define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1)
> #define PERF_EV_CAP_SIBLING BIT(2)
> +#define PERF_EV_CAP_READ_SCOPE BIT(3)
>
> #define SWEVENT_HLIST_BITS 8
> #define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS)
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 5e1877c4cb4c..c55294f34575 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4463,16 +4463,24 @@ struct perf_read_data {
> int ret;
> };
>
> +static inline const struct cpumask *perf_scope_cpu_topology_cpumask(unsigned int scope, int cpu);
> +
> static int __perf_event_read_cpu(struct perf_event *event, int event_cpu)
> {
> + int local_cpu = smp_processor_id();
> u16 local_pkg, event_pkg;
>
> if ((unsigned)event_cpu >= nr_cpu_ids)
> return event_cpu;
>
> - if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
> - int local_cpu = smp_processor_id();
> + if (event->group_caps & PERF_EV_CAP_READ_SCOPE) {
> + const struct cpumask *cpumask = perf_scope_cpu_topology_cpumask(event->pmu->scope, event_cpu);
> +
> + if (cpumask && cpumask_test_cpu(local_cpu, cpumask))
> + return local_cpu;
> + }
>
> + if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
I'm guessing the goal is to eventually remove this one, right?
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