Re: [PATCH V9 1/3] perf/x86/intel: Avoid pmu_disable/enable if !cpuc->enabled in sample read

Peter Zijlstra
2025-01-16T10:33:03Z

On Wed, Jan 15, 2025 at 10:43:16AM -0800, kan.liang@linux.intel.com wrote:
> From: Kan Liang <kan.liang@linux.intel.com>
>
> The WARN_ON(this_cpu_read(cpu_hw_events.enabled)) in the
> intel_pmu_save_and_restart_reload() is triggered, when sampling read
> topdown events.
>
> In a NMI handler, the cpu_hw_events.enabled is set and used to indicate
> the status of core PMU. The generic pmu->pmu_disable_count, updated in
> the perf_pmu_disable/enable pair, is not touched.
> However, the perf_pmu_disable/enable pair is invoked when sampling read
> in a NMI handler. The cpuc->enabled is mistakenly set by the
> perf_pmu_enable().
>
> Avoid perf_pmu_disable/enable() if the core PMU is already disabled.
>
> Fixes: 7b2c05a15d29 ("perf/x86/intel: Generic support for hardware TopDown metrics")
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> Cc: stable@vger.kernel.org
> ---
> arch/x86/events/intel/core.c | 7 +++++--
> arch/x86/events/intel/ds.c | 9 ++++++---
> 2 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 2a2824e9c50d..bce423ad3fad 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2778,15 +2778,18 @@ DEFINE_STATIC_CALL(intel_pmu_update_topdown_event, x86_perf_event_update);
> static void intel_pmu_read_topdown_event(struct perf_event *event)
> {
> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> + int pmu_enabled = cpuc->enabled;
>
> /* Only need to call update_topdown_event() once for group read. */
> if ((cpuc->txn_flags & PERF_PMU_TXN_READ) &&
> !is_slots_event(event))
> return;
>
> - perf_pmu_disable(event->pmu);
> + if (pmu_enabled)
> + perf_pmu_disable(event->pmu);
> static_call(intel_pmu_update_topdown_event)(event);
> - perf_pmu_enable(event->pmu);
> + if (pmu_enabled)
> + perf_pmu_enable(event->pmu);
> }
>
> static void intel_pmu_read_event(struct perf_event *event)
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index ba74e1198328..81b6ec8e824e 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -2096,11 +2096,14 @@ get_next_pebs_record_by_bit(void *base, void *top, int bit)
>
> void intel_pmu_auto_reload_read(struct perf_event *event)
> {
> - WARN_ON(!(event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD));
> + int pmu_enabled = this_cpu_read(cpu_hw_events.enabled);
>
> - perf_pmu_disable(event->pmu);
> + WARN_ON(!(event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD));
> + if (pmu_enabled)
> + perf_pmu_disable(event->pmu);
> intel_pmu_drain_pebs_buffer();
> - perf_pmu_enable(event->pmu);
> + if (pmu_enabled)
> + perf_pmu_enable(event->pmu);
> }

Hurmp.. would it not be nicer to merge that logic. Perhaps something
like so?

---
arch/x86/events/intel/core.c | 41 +++++++++++++++++++++++------------------
arch/x86/events/intel/ds.c | 11 +----------
arch/x86/events/perf_event.h | 2 +-
3 files changed, 25 insertions(+), 29 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 7601196d1d18..5b491a6815e6 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2785,28 +2785,33 @@ static u64 icl_update_topdown_event(struct perf_event *event)

DEFINE_STATIC_CALL(intel_pmu_update_topdown_event, x86_perf_event_update);

-static void intel_pmu_read_topdown_event(struct perf_event *event)
+static void intel_pmu_read_event(struct perf_event *event)
{
- struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+ if (event->hw.flags & (PERF_X86_EVENT_AUTO_RELOAD | PERF_X86_EVENT_TOPDOWN)) {
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+ bool pmu_enabled = cpuc->enabled;

- /* Only need to call update_topdown_event() once for group read. */
- if ((cpuc->txn_flags & PERF_PMU_TXN_READ) &&
- !is_slots_event(event))
- return;
+ /* Only need to call update_topdown_event() once for group read. */
+ if (is_topdown_event(event) && !is_slots_event(event) &&
+ (cpuc->txn_flags & PERF_PMU_TXN_READ))
+ return;

- perf_pmu_disable(event->pmu);
- static_call(intel_pmu_update_topdown_event)(event);
- perf_pmu_enable(event->pmu);
-}
+ cpuc->enabled = 0;
+ if (pmu_enabled)
+ intel_pmu_disable_all();

-static void intel_pmu_read_event(struct perf_event *event)
-{
- if (event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD)
- intel_pmu_auto_reload_read(event);
- else if (is_topdown_count(event))
- intel_pmu_read_topdown_event(event);
- else
- x86_perf_event_update(event);
+ if (is_topdown_event(event))
+ static_call(intel_pmu_update_topdown_event)(event);
+ else
+ intel_pmu_drain_pebs_buffer();
+
+ cpuc->enabled = pmu_enabled;
+ if (pmu_enabled)
+ intel_pmu_enable_all(0);
+ return;
+ }
+
+ x86_perf_event_update(event);
}

static void intel_pmu_enable_fixed(struct perf_event *event)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index ba74e1198328..050098c54ae7 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -953,7 +953,7 @@ int intel_pmu_drain_bts_buffer(void)
return 1;
}

-static inline void intel_pmu_drain_pebs_buffer(void)
+void intel_pmu_drain_pebs_buffer(void)
{
struct perf_sample_data data;

@@ -2094,15 +2094,6 @@ get_next_pebs_record_by_bit(void *base, void *top, int bit)
return NULL;
}

-void intel_pmu_auto_reload_read(struct perf_event *event)
-{
- WARN_ON(!(event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD));
-
- perf_pmu_disable(event->pmu);
- intel_pmu_drain_pebs_buffer();
- perf_pmu_enable(event->pmu);
-}
-
/*
* Special variant of intel_pmu_save_and_restart() for auto-reload.
*/
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 31c2771545a6..38b3e30f8988 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1643,7 +1643,7 @@ void intel_pmu_pebs_disable_all(void);

void intel_pmu_pebs_sched_task(struct perf_event_pmu_context *pmu_ctx, bool sched_in);

-void intel_pmu_auto_reload_read(struct perf_event *event);
+void intel_pmu_drain_pebs_buffer(void);

void intel_pmu_store_pebs_lbrs(struct lbr_entry *lbr);