linux-kernel - [PATCH 2/3] perf/amlogic: Fix large number of counter issue

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Date:   Thu, 9 Feb 2023 19:54:02 +0800
From:   Jiucheng Xu <jiucheng.xu@...ogic.com>
To:     Jiucheng Xu <jiucheng.xu@...ogic.com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
CC:     Jianxin Pan <jianxin.pan@...ogic.com>,
        Kelvin Zhang <kelvin.zhang@...ogic.com>,
        Chris Healy <cphealy@...il.com>,
        Chris Healy <healych@...zon.com>,
        <linux-amlogic@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/3] perf/amlogic: Fix large number of counter issue

When use 1ms interval, very large number of counter happens
once in a while as below:

25.968654513 281474976710655.84 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/
26.118657346 281474976710655.88 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/
26.180137180 281474976710655.66 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/

Root cause is the race between irq handler
and pmu.read callback. Use spin lock to protect the sw&hw
counters.

Signed-off-by: Jiucheng Xu <jiucheng.xu@...ogic.com>
---
 drivers/perf/amlogic/meson_ddr_pmu_core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/perf/amlogic/meson_ddr_pmu_core.c b/drivers/perf/amlogic/meson_ddr_pmu_core.c
index 0b24dee1ed3c..9b2e5d5c0626 100644
--- a/drivers/perf/amlogic/meson_ddr_pmu_core.c
+++ b/drivers/perf/amlogic/meson_ddr_pmu_core.c
@@ -14,6 +14,7 @@
 #include <linux/perf_event.h>
 #include <linux/platform_device.h>
 #include <linux/printk.h>
+#include <linux/spinlock.h>
 #include <linux/sysfs.h>
 #include <linux/types.h>
 
@@ -23,6 +24,7 @@ struct ddr_pmu {
 	struct pmu pmu;
 	struct dmc_info info;
 	struct dmc_counter counters;	/* save counters from hw */
+	spinlock_t lock;		/* protect hw/sw counter */
 	bool pmu_enabled;
 	struct device *dev;
 	char *name;
@@ -92,10 +94,12 @@ static void meson_ddr_perf_event_update(struct perf_event *event)
 	int idx;
 	int chann_nr = pmu->info.hw_info->chann_nr;
 
+	spin_lock(&pmu->lock);
 	/* get the remain counters in register. */
 	pmu->info.hw_info->get_counters(&pmu->info, &dc);
 
 	ddr_cnt_addition(&sum_dc, &pmu->counters, &dc, chann_nr);
+	spin_unlock(&pmu->lock);
 
 	switch (event->attr.config) {
 	case ALL_CHAN_COUNTER_ID:
@@ -355,6 +359,7 @@ static irqreturn_t dmc_irq_handler(int irq, void *dev_id)
 
 	pmu = dmc_info_to_pmu(info);
 
+	spin_lock(&pmu->lock);
 	if (info->hw_info->irq_handler(info, &counters) != 0)
 		goto out;
 
@@ -372,6 +377,8 @@ static irqreturn_t dmc_irq_handler(int irq, void *dev_id)
 		 * it in ISR to support continue mode.
 		 */
 		info->hw_info->enable(info);
+out:
+	spin_unlock(&pmu->lock);
 
 	dev_dbg(pmu->dev, "counts: %llu %llu %llu, %llu, %llu, %llu\t\t"
 			"sum: %llu %llu %llu, %llu, %llu, %llu\n",
@@ -388,7 +395,7 @@ static irqreturn_t dmc_irq_handler(int irq, void *dev_id)
 			pmu->counters.channel_cnt[1],
 			pmu->counters.channel_cnt[2],
 			pmu->counters.channel_cnt[3]);
-out:
+
 	return IRQ_HANDLED;
 }
 
@@ -539,6 +546,7 @@ int meson_ddr_pmu_create(struct platform_device *pdev)
 	pmu->name = name;
 	pmu->dev = &pdev->dev;
 	pmu->pmu_enabled = false;
+	spin_lock_init(&pmu->lock);
 
 	platform_set_drvdata(pdev, pmu);
 
-- 
2.25.1