[PATCH] cpufreq_conservative: make for_each_cpu() safe

All these changes should make cpufreq_conservative safe in regards to the x86
for_each_cpu cpumask.h changes and whatnot.

Whilst making it safe a number of pointless for loops related to the cpu
mask's were removed.  I was never comfortable with all those for loops,
especially as the iteration is over the same data again and again for each
CPU you had in a single poll, an O(n^2) outcome to frequency scaling.

The approach I use is to assume by default no CPU's exist and it sets the
requested_freq to zero as a kind of flag, the reasoning is in the source ;)
If the CPU is queried and requested_freq is zero then it initialises the
variable to current_freq and then continues as if nothing happened which
should be the same net effect as before?

Signed-off-by: Alexander Clouter <alex-kernel@digriz.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

1 files changed, 42 insertions, 49 deletions

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index 3ca3cf061642..7498f2506ade 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -294,31 +294,40 @@ static struct attribute_group dbs_attr_group = {
 static void dbs_check_cpu(int cpu)
 {
         unsigned int idle_ticks, up_idle_ticks, down_idle_ticks;
+        unsigned int tmp_idle_ticks, total_idle_ticks;
         unsigned int freq_step;
         unsigned int freq_down_sampling_rate;
-        static int down_skip[NR_CPUS];
-        static int requested_freq[NR_CPUS];
-        static unsigned short init_flag = 0;
-        struct cpu_dbs_info_s *this_dbs_info;
-        struct cpu_dbs_info_s *dbs_info;
-
+        static unsigned short down_skip[NR_CPUS];
+        static unsigned int requested_freq[NR_CPUS];
+        static unsigned int init_flag = NR_CPUS;
+        struct cpu_dbs_info_s *this_dbs_info = &per_cpu(cpu_dbs_info, cpu);
         struct cpufreq_policy *policy;
-        unsigned int j;
 
-        this_dbs_info = &per_cpu(cpu_dbs_info, cpu);
         if (!this_dbs_info->enable)
                 return;
 
-        policy = this_dbs_info->cur_policy;
-
-        if ( init_flag == 0 ) {
-                for_each_online_cpu(j) {
-                        dbs_info = &per_cpu(cpu_dbs_info, j);
-                        requested_freq[j] = dbs_info->cur_policy->cur;
+        if ( init_flag != 0 ) {
+                for_each_cpu(init_flag) {
+                        down_skip[init_flag] = 0;
+                        /* I doubt a CPU exists with a freq of 0hz :) */
+                        requested_freq[init_flag] = 0;
                 }
-                init_flag = 1;
+                init_flag = 0;
         }
         
+        /*
+         * If its a freshly initialised cpu we setup requested_freq.  This
+         * check could be avoided if we did not care about a first time
+         * stunted increase in CPU speed when there is a load.  I feel we
+         * should be initialising this to something.  The removal of a CPU
+         * is not a problem, after a short time the CPU should settle down
+         * to a 'natural' frequency.
+         */
+        if (requested_freq[cpu] == 0)
+                requested_freq[cpu] = this_dbs_info->cur_policy->cur;
+
+        policy = this_dbs_info->cur_policy;
+
         /* 
          * The default safe range is 20% to 80% 
          * Every sampling_rate, we check
@@ -335,20 +344,15 @@ static void dbs_check_cpu(int cpu)
 
         /* Check for frequency increase */
         idle_ticks = UINT_MAX;
-        for_each_cpu_mask(j, policy->cpus) {
-                unsigned int tmp_idle_ticks, total_idle_ticks;
-                struct cpu_dbs_info_s *j_dbs_info;
 
-                j_dbs_info = &per_cpu(cpu_dbs_info, j);
-                /* Check for frequency increase */
-                total_idle_ticks = get_cpu_idle_time(j);
-                tmp_idle_ticks = total_idle_ticks -
-                        j_dbs_info->prev_cpu_idle_up;
-                j_dbs_info->prev_cpu_idle_up = total_idle_ticks;
-
-                if (tmp_idle_ticks < idle_ticks)
-                        idle_ticks = tmp_idle_ticks;
-        }
+        /* Check for frequency increase */
+        total_idle_ticks = get_cpu_idle_time(cpu);
+        tmp_idle_ticks = total_idle_ticks -
+                this_dbs_info->prev_cpu_idle_up;
+        this_dbs_info->prev_cpu_idle_up = total_idle_ticks;
+
+        if (tmp_idle_ticks < idle_ticks)
+                idle_ticks = tmp_idle_ticks;
 
         /* Scale idle ticks by 100 and compare with up and down ticks */
         idle_ticks *= 100;
@@ -357,13 +361,9 @@ static void dbs_check_cpu(int cpu)
 
         if (idle_ticks < up_idle_ticks) {
                 down_skip[cpu] = 0;
-                for_each_cpu_mask(j, policy->cpus) {
-                        struct cpu_dbs_info_s *j_dbs_info;
+                this_dbs_info->prev_cpu_idle_down =
+                        this_dbs_info->prev_cpu_idle_up;
 
-                        j_dbs_info = &per_cpu(cpu_dbs_info, j);
-                        j_dbs_info->prev_cpu_idle_down = 
-                                        j_dbs_info->prev_cpu_idle_up;
-                }
                 /* if we are already at full speed then break out early */
                 if (requested_freq[cpu] == policy->max)
                         return;
@@ -388,21 +388,14 @@ static void dbs_check_cpu(int cpu)
         if (down_skip[cpu] < dbs_tuners_ins.sampling_down_factor)
                 return;
 
-        idle_ticks = UINT_MAX;
-        for_each_cpu_mask(j, policy->cpus) {
-                unsigned int tmp_idle_ticks, total_idle_ticks;
-                struct cpu_dbs_info_s *j_dbs_info;
+        /* Check for frequency decrease */
+        total_idle_ticks = this_dbs_info->prev_cpu_idle_up;
+        tmp_idle_ticks = total_idle_ticks -
+                this_dbs_info->prev_cpu_idle_down;
+        this_dbs_info->prev_cpu_idle_down = total_idle_ticks;
 
-                j_dbs_info = &per_cpu(cpu_dbs_info, j);
-                /* Check for frequency decrease */
-                total_idle_ticks = j_dbs_info->prev_cpu_idle_up;
-                tmp_idle_ticks = total_idle_ticks -
-                        j_dbs_info->prev_cpu_idle_down;
-                j_dbs_info->prev_cpu_idle_down = total_idle_ticks;
-
-                if (tmp_idle_ticks < idle_ticks)
-                        idle_ticks = tmp_idle_ticks;
-        }
+        if (tmp_idle_ticks < idle_ticks)
+                idle_ticks = tmp_idle_ticks;
 
         /* Scale idle ticks by 100 and compare with up and down ticks */
         idle_ticks *= 100;
@@ -491,7 +484,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                         j_dbs_info = &per_cpu(cpu_dbs_info, j);
                         j_dbs_info->cur_policy = policy;
                 
-                        j_dbs_info->prev_cpu_idle_up = get_cpu_idle_time(j);
+                        j_dbs_info->prev_cpu_idle_up = get_cpu_idle_time(cpu);
                         j_dbs_info->prev_cpu_idle_down
                                 = j_dbs_info->prev_cpu_idle_up;
                 }