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 frequencies, 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@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
[ rjw: Fix typo in changelog, remove redundant parens ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
index 55c7ffd..a33df3c 100644 (file)
--- 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;