linux-kernel - [PATCH v2 2/5] perf/x86/intel/uncore: Use HRTIMER_MODE

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Message-ID: <0ad4698465077225769e8edd5b2c7e8f48f636d5.1744906694.git.sandipan.das@amd.com>
Date: Fri, 18 Apr 2025 09:13:00 +0530
From: Sandipan Das <sandipan.das@....com>
To: <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
	<namhyung@...nel.org>, <mark.rutland@....com>,
	<alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
	<irogers@...gle.com>, <adrian.hunter@...el.com>, <kan.liang@...ux.intel.com>,
	<tglx@...utronix.de>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, <hpa@...or.com>, <eranian@...gle.com>,
	<songliubraving@...a.com>, <ravi.bangoria@....com>, <ananth.narayan@....com>,
	<sandipan.das@....com>
Subject: [PATCH v2 2/5] perf/x86/intel/uncore: Use HRTIMER_MODE_HARD for detecting overflows

Hrtimer handlers can be deferred to softirq context and affect timely
detection of counter overflows. Hence switch to HRTIMER_MODE_HARD.

Disabling and re-enabling IRQs in the hrtimer handler is not required
as pmu->start() and pmu->stop() can no longer intervene while updating
event->hw.prev_count.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Sandipan Das <sandipan.das@....com>
---
 arch/x86/events/intel/uncore.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
index a34e50fc4a8f..5811e172f721 100644
--- a/arch/x86/events/intel/uncore.c
+++ b/arch/x86/events/intel/uncore.c
@@ -305,17 +305,11 @@ static enum hrtimer_restart uncore_pmu_hrtimer(struct hrtimer *hrtimer)
 {
 	struct intel_uncore_box *box;
 	struct perf_event *event;
-	unsigned long flags;
 	int bit;
 
 	box = container_of(hrtimer, struct intel_uncore_box, hrtimer);
 	if (!box->n_active || box->cpu != smp_processor_id())
 		return HRTIMER_NORESTART;
-	/*
-	 * disable local interrupt to prevent uncore_pmu_event_start/stop
-	 * to interrupt the update process
-	 */
-	local_irq_save(flags);
 
 	/*
 	 * handle boxes with an active event list as opposed to active
@@ -328,8 +322,6 @@ static enum hrtimer_restart uncore_pmu_hrtimer(struct hrtimer *hrtimer)
 	for_each_set_bit(bit, box->active_mask, UNCORE_PMC_IDX_MAX)
 		uncore_perf_event_update(box, box->events[bit]);
 
-	local_irq_restore(flags);
-
 	hrtimer_forward_now(hrtimer, ns_to_ktime(box->hrtimer_duration));
 	return HRTIMER_RESTART;
 }
@@ -337,7 +329,7 @@ static enum hrtimer_restart uncore_pmu_hrtimer(struct hrtimer *hrtimer)
 void uncore_pmu_start_hrtimer(struct intel_uncore_box *box)
 {
 	hrtimer_start(&box->hrtimer, ns_to_ktime(box->hrtimer_duration),
-		      HRTIMER_MODE_REL_PINNED);
+		      HRTIMER_MODE_REL_PINNED_HARD);
 }
 
 void uncore_pmu_cancel_hrtimer(struct intel_uncore_box *box)
@@ -347,7 +339,7 @@ void uncore_pmu_cancel_hrtimer(struct intel_uncore_box *box)
 
 static void uncore_pmu_init_hrtimer(struct intel_uncore_box *box)
 {
-	hrtimer_setup(&box->hrtimer, uncore_pmu_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrtimer_setup(&box->hrtimer, uncore_pmu_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
 }
 
 static struct intel_uncore_box *uncore_alloc_box(struct intel_uncore_type *type,
-- 
2.43.0