ARCv2: perf: tweak overflow interrupt

Current perf ISR loops thru all 32 counters, checking for each if it
caused the interrupt. Instead only loop thru counters which actually
interrupted (typically 1).
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/kernel/perf_event.c

@@ -377,21 +377,22 @@ static irqreturn_t arc_pmu_intr(int irq, void *dev)
 	struct perf_sample_data data;
 	struct arc_pmu_cpu *pmu_cpu = this_cpu_ptr(&arc_pmu_cpu);
 	struct pt_regs *regs;
-	int active_ints;
+	unsigned int active_ints;
 	int idx;
 
 	arc_pmu_disable(&arc_pmu->pmu);
 
 	active_ints = read_aux_reg(ARC_REG_PCT_INT_ACT);
+	if (!active_ints)
+		goto done;
 
 	regs = get_irq_regs();
 
-	for (idx = 0; idx < arc_pmu->n_counters; idx++) {
-		struct perf_event *event = pmu_cpu->act_counter[idx];
+	do {
+		struct perf_event *event;
 		struct hw_perf_event *hwc;
 
-		if (!(active_ints & (1 << idx)))
-			continue;
+		idx = __ffs(active_ints);
 
 		/* Reset interrupt flag by writing of 1 */
 		write_aux_reg(ARC_REG_PCT_INT_ACT, 1 << idx);
@@ -404,19 +405,22 @@ static irqreturn_t arc_pmu_intr(int irq, void *dev)
 		write_aux_reg(ARC_REG_PCT_INT_CTRL,
 			read_aux_reg(ARC_REG_PCT_INT_CTRL) | (1 << idx));
 
+		event = pmu_cpu->act_counter[idx];
 		hwc = &event->hw;
 
 		WARN_ON_ONCE(hwc->idx != idx);
 
 		arc_perf_event_update(event, &event->hw, event->hw.idx);
 		perf_sample_data_init(&data, 0, hwc->last_period);
-		if (!arc_pmu_event_set_period(event))
-			continue;
-
+		if (arc_pmu_event_set_period(event)) {
 			if (perf_event_overflow(event, &data, regs))
 				arc_pmu_stop(event, 0);
 		}
 
+		active_ints &= ~(1U << idx);
+	} while (active_ints);
+
+done:
 	arc_pmu_enable(&arc_pmu->pmu);
 
 	return IRQ_HANDLED;