cpufreq: conservative: Fix the logic in frequency decrease checking
PATCH 2/3 cpufreq: conservative: Fix the logic in frequency decrease checking
When we evaluate the CPU load for frequency decrease we have to compare the load against down_threshold. There is no need to subtract 10 points from down_threshold.
Instead, we have to use the default down_threshold or user's selection unmodified.
--- drivers/cpufreq/cpufreq_conservative.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
drivers/cpufreq/cpufreq_conservative.c +2 -6
@@ -92,12 +92,8 @@ static void cs_check_cpu(int cpu, unsigned int load)return ; dbs_info->down_skip =0 ; -/* -* The optimal frequency is the frequency that is the lowest that can -* support the current CPU usage without triggering the up policy. To be -* safe, we focus 10 points under the threshold. -*/ -if (load < (cs_tuners.down_threshold -10 )) { +/* Check for frequency decrease */ +if (load < cs_tuners.down_threshold) { freq_target = (cs_tuners.freq_step * policy->max) /100 ; dbs_info->requested_freq -= freq_target;
Signature · 1 line
1.8.1.4
Quoted 11 lines · Stratos Karafotis
When we evaluate the CPU load for frequency decrease we have to compare the load against
down_threshold. There is no need to subtract 10 points fromdown_threshold.Instead, we have to use the default
down_thresholdor user's selection unmodified.Signed-off-by Stratos Karafotis <[email protected]>--- drivers/cpufreq/cpufreq_conservative.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
The "10" sounds like an attempt to add some hysteresis to the up/down decisionmaking. If you take it out, you should make sure you don't get into situations where you're continually switching rapidly between two frequencies. (In the ondemand governor some care was also taken to avoid the cost of doing a CPU idleness evaluation counting towards the CPU looking busy enough to upshift; I am not familiar enough with Conservative to know whether that is a problem for it too).
DCN
Quoted 31 lines · Stratos Karafotis
When we evaluate the CPU load for frequency decrease we have to compare the load against
down_threshold. There is no need to subtract 10 points fromdown_threshold.Instead, we have to use the default
down_thresholdor user's selection unmodified.Signed-off-by Stratos Karafotis <[email protected]>--- drivers/cpufreq/cpufreq_conservative.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)drivers/cpufreq/cpufreq_conservative.c +2
-6@@ -92,12 +92,8 @@ static void cs_check_cpu(int cpu, unsigned int load)return ; dbs_info->down_skip =0 ; -/* -* The optimal frequency is the frequency that is the lowest that can -* support the current CPU usage without triggering the up policy. To be -* safe, we focus 10 points under the threshold. -*/ -if (load < (cs_tuners.down_threshold -10 )) { +/* Check for frequency decrease */ +if (load < cs_tuners.down_threshold) { freq_target = (cs_tuners.freq_step * policy->max) /100 ; dbs_info->requested_freq -= freq_target;
Quoted 3 lines · David C Niemi
The "10" sounds like an attempt to add some hysteresis to the up/down decisionmaking. If you take it out, you should make sure you don't get into situations where you're continually switching rapidly between two frequencies. (In the ondemand governor some care was also taken to avoid the cost of doing a CPU idleness evaluation counting towards the CPU looking busy enough to upshift; I am not familiar enough with Conservative to know whether that is a problem for it too).
DCN
This is true for ondemand but, as you know, there is a separate tunable (down_threshold) in conservative with default value 20.
It's independent from up_threshold (default 80), so I believe there is no need to add a hysteresis.
Also, if we subtract 10 from down_threshold, we change user's decision about this threshold. For example, if user sets down_threshold to 25, wants this value to 25 not to 15.
Checking the initial commit of conservative governor, we can see that it was not use hysteresis factor. This was added later (by mistake in my opinion) as an attempt to make conservative to function similar to ondemand.