linux-kernel - [PATCH] cpufreq: stats: Improve the performance of cpufreq_stats_create

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Message-ID: <20230818095000.937633-1-liaochang1@huawei.com>
Date:   Fri, 18 Aug 2023 09:50:00 +0000
From:   Liao Chang <liaochang1@...wei.com>
To:     <rafael@...nel.org>, <viresh.kumar@...aro.org>
CC:     <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] cpufreq: stats: Improve the performance of cpufreq_stats_create_table()

In the worst case, the freq_table of policy data is not sorted and
contains duplicate frequencies, this means that it needs to iterate
through the entire freq_table of policy to ensure each frequency is
unique in the freq_table of stats data, this has a time complexity of
O(N^2), where N is the number of frequencies in the freq_table of
policy.

However, if the policy.freq_table is already sorted and contains no
duplicate frequencices, it can reduce the time complexity of creating
stats.freq_table to O(N), the 'freq_table_sorted' field of policy data
can be used to indicate whether the policy.freq_table is sorted.

Signed-off-by: Liao Chang <liaochang1@...wei.com>
---
 drivers/cpufreq/cpufreq_stats.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
index 55c7ffd37d1c..fcb74050711a 100644
--- a/drivers/cpufreq/cpufreq_stats.c
+++ b/drivers/cpufreq/cpufreq_stats.c
@@ -243,7 +243,8 @@ void cpufreq_stats_create_table(struct cpufreq_policy *policy)

 	/* Find valid-unique entries */
 	cpufreq_for_each_valid_entry(pos, policy->freq_table)
-		if (freq_table_get_index(stats, pos->frequency) == -1)
+		if ((policy->freq_table_sorted != CPUFREQ_TABLE_UNSORTED) ||
+		    (freq_table_get_index(stats, pos->frequency) == -1))
 			stats->freq_table[i++] = pos->frequency;

 	stats->state_num = i;
-- 
2.34.1