add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/drivers/cpufreq/cpufreq_stats.c
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@@ -1,12 +1,9 @@
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+// SPDX-License-Identifier: GPL-2.0-only
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 /*
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  *  drivers/cpufreq/cpufreq_stats.c
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  *
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  *  Copyright (C) 2003-2004 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>.
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  *  (C) 2004 Zou Nan hai <nanhai.zou@intel.com>.
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- *
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- * This program is free software; you can redistribute it and/or modify
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- * it under the terms of the GNU General Public License version 2 as
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- * published by the Free Software Foundation.
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  */
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 #include <linux/cpu.h>
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@@ -14,7 +11,6 @@
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 #include <linux/module.h>
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 #include <linux/slab.h>
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13
 
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-static DEFINE_SPINLOCK(cpufreq_stats_lock);
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 struct cpufreq_stats {
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 	unsigned int total_trans;
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@@ -25,19 +21,22 @@
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 	u64 *time_in_state;
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 	unsigned int *freq_table;
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 	unsigned int *trans_table;
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+
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+	/* Deferred reset */
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+	unsigned int reset_pending;
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+	unsigned long long reset_time;
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 };
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-static void cpufreq_stats_update(struct cpufreq_stats *stats)
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+static void cpufreq_stats_update(struct cpufreq_stats *stats,
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+				 unsigned long long time)
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 {
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 	unsigned long long cur_time = get_jiffies_64();
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-	spin_lock(&cpufreq_stats_lock);
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-	stats->time_in_state[stats->last_index] += cur_time - stats->last_time;
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+	stats->time_in_state[stats->last_index] += cur_time - time;
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 	stats->last_time = cur_time;
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-	spin_unlock(&cpufreq_stats_lock);
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 }
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-static void cpufreq_stats_clear_table(struct cpufreq_stats *stats)
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+static void cpufreq_stats_reset_table(struct cpufreq_stats *stats)
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 {
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 	unsigned int count = stats->max_state;
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@@ -45,77 +44,124 @@
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 	memset(stats->trans_table, 0, count * count * sizeof(int));
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 	stats->last_time = get_jiffies_64();
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 	stats->total_trans = 0;
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+
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+	/* Adjust for the time elapsed since reset was requested */
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+	WRITE_ONCE(stats->reset_pending, 0);
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+	/*
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+	 * Prevent the reset_time read from being reordered before the
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+	 * reset_pending accesses in cpufreq_stats_record_transition().
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+	 */
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+	smp_rmb();
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+	cpufreq_stats_update(stats, READ_ONCE(stats->reset_time));
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 }
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 static ssize_t show_total_trans(struct cpufreq_policy *policy, char *buf)
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 {
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-	return sprintf(buf, "%d\n", policy->stats->total_trans);
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+	struct cpufreq_stats *stats = policy->stats;
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+
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+	if (READ_ONCE(stats->reset_pending))
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+		return sprintf(buf, "%d\n", 0);
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+	else
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+		return sprintf(buf, "%u\n", stats->total_trans);
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 }
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+cpufreq_freq_attr_ro(total_trans);
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 static ssize_t show_time_in_state(struct cpufreq_policy *policy, char *buf)
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 {
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 	struct cpufreq_stats *stats = policy->stats;
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+	bool pending = READ_ONCE(stats->reset_pending);
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+	unsigned long long time;
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 	ssize_t len = 0;
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 	int i;
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-	if (policy->fast_switch_enabled)
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-		return 0;
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-
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-	cpufreq_stats_update(stats);
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 	for (i = 0; i < stats->state_num; i++) {
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+		if (pending) {
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+			if (i == stats->last_index) {
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+				/*
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+				 * Prevent the reset_time read from occurring
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+				 * before the reset_pending read above.
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+				 */
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+				smp_rmb();
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+				time = get_jiffies_64() - READ_ONCE(stats->reset_time);
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+			} else {
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+				time = 0;
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+			}
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+		} else {
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+			time = stats->time_in_state[i];
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+			if (i == stats->last_index)
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+				time += get_jiffies_64() - stats->last_time;
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+		}
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+
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 		len += sprintf(buf + len, "%u %llu\n", stats->freq_table[i],
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-			(unsigned long long)
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-			jiffies_64_to_clock_t(stats->time_in_state[i]));
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+			       jiffies_64_to_clock_t(time));
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 	}
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 	return len;
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 }
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+cpufreq_freq_attr_ro(time_in_state);
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+/* We don't care what is written to the attribute */
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 static ssize_t store_reset(struct cpufreq_policy *policy, const char *buf,
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 			   size_t count)
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 {
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-	/* We don't care what is written to the attribute. */
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-	cpufreq_stats_clear_table(policy->stats);
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+	struct cpufreq_stats *stats = policy->stats;
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+
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+	/*
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+	 * Defer resetting of stats to cpufreq_stats_record_transition() to
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+	 * avoid races.
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+	 */
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+	WRITE_ONCE(stats->reset_time, get_jiffies_64());
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+	/*
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+	 * The memory barrier below is to prevent the readers of reset_time from
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+	 * seeing a stale or partially updated value.
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+	 */
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+	smp_wmb();
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+	WRITE_ONCE(stats->reset_pending, 1);
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+
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 	return count;
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 }
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+cpufreq_freq_attr_wo(reset);
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 static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
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 {
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 	struct cpufreq_stats *stats = policy->stats;
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+	bool pending = READ_ONCE(stats->reset_pending);
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 	ssize_t len = 0;
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-	int i, j;
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+	int i, j, count;
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-	if (policy->fast_switch_enabled)
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-		return 0;
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-
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-	len += snprintf(buf + len, PAGE_SIZE - len, "   From  :    To\n");
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-	len += snprintf(buf + len, PAGE_SIZE - len, "         : ");
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+	len += scnprintf(buf + len, PAGE_SIZE - len, "   From  :    To\n");
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+	len += scnprintf(buf + len, PAGE_SIZE - len, "         : ");
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 	for (i = 0; i < stats->state_num; i++) {
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 		if (len >= PAGE_SIZE)
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 			break;
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-		len += snprintf(buf + len, PAGE_SIZE - len, "%9u ",
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+		len += scnprintf(buf + len, PAGE_SIZE - len, "%9u ",
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 				stats->freq_table[i]);
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 	}
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 	if (len >= PAGE_SIZE)
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 		return PAGE_SIZE;
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-	len += snprintf(buf + len, PAGE_SIZE - len, "\n");
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+	len += scnprintf(buf + len, PAGE_SIZE - len, "\n");
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 	for (i = 0; i < stats->state_num; i++) {
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 		if (len >= PAGE_SIZE)
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 			break;
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-		len += snprintf(buf + len, PAGE_SIZE - len, "%9u: ",
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+		len += scnprintf(buf + len, PAGE_SIZE - len, "%9u: ",
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 				stats->freq_table[i]);
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 		for (j = 0; j < stats->state_num; j++) {
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 			if (len >= PAGE_SIZE)
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 				break;
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-			len += snprintf(buf + len, PAGE_SIZE - len, "%9u ",
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-					stats->trans_table[i*stats->max_state+j]);
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+
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+			if (pending)
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+				count = 0;
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+			else
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+				count = stats->trans_table[i * stats->max_state + j];
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+
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+			len += scnprintf(buf + len, PAGE_SIZE - len, "%9u ", count);
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 		}
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 		if (len >= PAGE_SIZE)
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 			break;
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-		len += snprintf(buf + len, PAGE_SIZE - len, "\n");
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+		len += scnprintf(buf + len, PAGE_SIZE - len, "\n");
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 	}
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 	if (len >= PAGE_SIZE) {
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@@ -125,10 +171,6 @@
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 	return len;
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 }
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 cpufreq_freq_attr_ro(trans_table);
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-
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-cpufreq_freq_attr_ro(total_trans);
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-cpufreq_freq_attr_ro(time_in_state);
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-cpufreq_freq_attr_wo(reset);
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 static struct attribute *default_attrs[] = {
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 	&total_trans.attr,
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@@ -228,19 +270,20 @@
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 	struct cpufreq_stats *stats = policy->stats;
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 	int old_index, new_index;
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-	if (!stats) {
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-		pr_debug("%s: No stats found\n", __func__);
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+	if (unlikely(!stats))
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 		return;
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-	}
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+
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+	if (unlikely(READ_ONCE(stats->reset_pending)))
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+		cpufreq_stats_reset_table(stats);
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 	old_index = stats->last_index;
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 	new_index = freq_table_get_index(stats, new_freq);
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 	/* We can't do stats->time_in_state[-1]= .. */
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-	if (old_index == -1 || new_index == -1 || old_index == new_index)
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+	if (unlikely(old_index == -1 || new_index == -1 || old_index == new_index))
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 		return;
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-	cpufreq_stats_update(stats);
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+	cpufreq_stats_update(stats, stats->last_time);
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 	stats->last_index = new_index;
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 	stats->trans_table[old_index * stats->max_state + new_index]++;