linux-kernel - [PATCH 4/5] perf/x86: Change x86_pmu::limit

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Message-ID: <20220511142345.289907761@infradead.org>
Date:   Wed, 11 May 2022 16:20:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, kan.liang@...ux.intel.com, eranian@...gle.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org
Subject: [PATCH 4/5] perf/x86: Change x86_pmu::limit_period signature

In preparation for making it a static_call, change the signature.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/events/amd/core.c   |    8 +++-----
 arch/x86/events/core.c       |   18 ++++++++----------
 arch/x86/events/intel/core.c |   19 ++++++++-----------
 arch/x86/events/perf_event.h |    2 +-
 4 files changed, 20 insertions(+), 27 deletions(-)

--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -1258,16 +1258,14 @@ static void amd_pmu_sched_task(struct pe
 		amd_pmu_brs_sched_task(ctx, sched_in);
 }
 
-static u64 amd_pmu_limit_period(struct perf_event *event, u64 left)
+static void amd_pmu_limit_period(struct perf_event *event, s64 *left)
 {
 	/*
 	 * Decrease period by the depth of the BRS feature to get the last N
 	 * taken branches and approximate the desired period
 	 */
-	if (has_branch_stack(event) && left > x86_pmu.lbr_nr)
-		left -= x86_pmu.lbr_nr;
-
-	return left;
+	if (has_branch_stack(event) && *left > x86_pmu.lbr_nr)
+		*left -= x86_pmu.lbr_nr;
 }
 
 static __initconst const struct x86_pmu amd_pmu = {
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -621,8 +621,9 @@ int x86_pmu_hw_config(struct perf_event
 		event->hw.config |= event->attr.config & X86_RAW_EVENT_MASK;
 
 	if (event->attr.sample_period && x86_pmu.limit_period) {
-		if (x86_pmu.limit_period(event, event->attr.sample_period) >
-				event->attr.sample_period)
+		s64 left = event->attr.sample_period;
+		x86_pmu.limit_period(event, &left);
+		if (left > event->attr.sample_period)
 			return -EINVAL;
 	}
 
@@ -1386,19 +1387,14 @@ int x86_perf_event_set_period(struct per
 		hwc->last_period = period;
 		ret = 1;
 	}
-	/*
-	 * Quirk: certain CPUs dont like it if just 1 hw_event is left:
-	 */
-	if (unlikely(left < 2))
-		left = 2;
 
 	if (left > x86_pmu.max_period)
 		left = x86_pmu.max_period;
 
 	if (x86_pmu.limit_period)
-		left = x86_pmu.limit_period(event, left);
+		x86_pmu.limit_period(event, &left);
 
-	per_cpu(pmc_prev_left[idx], smp_processor_id()) = left;
+	this_cpu_write(pmc_prev_left[idx], left);
 
 	/*
 	 * The hw event starts counting from this event offset,
@@ -2672,7 +2668,9 @@ static int x86_pmu_check_period(struct p
 		return -EINVAL;
 
 	if (value && x86_pmu.limit_period) {
-		if (x86_pmu.limit_period(event, value) > value)
+		s64 left = value;
+		x86_pmu.limit_period(event, &left);
+		if (left > value)
 			return -EINVAL;
 	}
 
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4244,28 +4244,25 @@ static u8 adl_get_hybrid_cpu_type(void)
  * Therefore the effective (average) period matches the requested period,
  * despite coarser hardware granularity.
  */
-static u64 bdw_limit_period(struct perf_event *event, u64 left)
+static void bdw_limit_period(struct perf_event *event, s64 *left)
 {
 	if ((event->hw.config & INTEL_ARCH_EVENT_MASK) ==
 			X86_CONFIG(.event=0xc0, .umask=0x01)) {
-		if (left < 128)
-			left = 128;
-		left &= ~0x3fULL;
+		if (*left < 128)
+			*left = 128;
+		*left &= ~0x3fULL;
 	}
-	return left;
 }
 
-static u64 nhm_limit_period(struct perf_event *event, u64 left)
+static void nhm_limit_period(struct perf_event *event, s64 *left)
 {
-	return max(left, 32ULL);
+	*left = max(*left, 32LL);
 }
 
-static u64 spr_limit_period(struct perf_event *event, u64 left)
+static void spr_limit_period(struct perf_event *event, s64 *left)
 {
 	if (event->attr.precise_ip == 3)
-		return max(left, 128ULL);
-
-	return left;
+		*left = max(*left, 128LL);
 }
 
 PMU_FORMAT_ATTR(event,	"config:0-7"	);
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -773,7 +773,7 @@ struct x86_pmu {
 	struct event_constraint *event_constraints;
 	struct x86_pmu_quirk *quirks;
 	int		perfctr_second_write;
-	u64		(*limit_period)(struct perf_event *event, u64 l);
+	void		(*limit_period)(struct perf_event *event, s64 *l);
 
 	/* PMI handler bits */
 	unsigned int	late_ack		:1,