diff options
Diffstat (limited to 'Documentation/cpu-freq')
-rw-r--r-- | Documentation/cpu-freq/governors.txt | 26 |
1 files changed, 14 insertions, 12 deletions
diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt index ce73f3eb5ddb..aed082f49d09 100644 --- a/Documentation/cpu-freq/governors.txt +++ b/Documentation/cpu-freq/governors.txt | |||
@@ -119,10 +119,6 @@ want the kernel to look at the CPU usage and to make decisions on | |||
119 | what to do about the frequency. Typically this is set to values of | 119 | what to do about the frequency. Typically this is set to values of |
120 | around '10000' or more. It's default value is (cmp. with users-guide.txt): | 120 | around '10000' or more. It's default value is (cmp. with users-guide.txt): |
121 | transition_latency * 1000 | 121 | transition_latency * 1000 |
122 | The lowest value you can set is: | ||
123 | transition_latency * 100 or it may get restricted to a value where it | ||
124 | makes not sense for the kernel anymore to poll that often which depends | ||
125 | on your HZ config variable (HZ=1000: max=20000us, HZ=250: max=5000). | ||
126 | Be aware that transition latency is in ns and sampling_rate is in us, so you | 122 | Be aware that transition latency is in ns and sampling_rate is in us, so you |
127 | get the same sysfs value by default. | 123 | get the same sysfs value by default. |
128 | Sampling rate should always get adjusted considering the transition latency | 124 | Sampling rate should always get adjusted considering the transition latency |
@@ -131,14 +127,20 @@ in the bash (as said, 1000 is default), do: | |||
131 | echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) \ | 127 | echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) \ |
132 | >ondemand/sampling_rate | 128 | >ondemand/sampling_rate |
133 | 129 | ||
134 | show_sampling_rate_(min|max): THIS INTERFACE IS DEPRECATED, DON'T USE IT. | 130 | show_sampling_rate_min: |
135 | You can use wider ranges now and the general | 131 | The sampling rate is limited by the HW transition latency: |
136 | cpuinfo_transition_latency variable (cmp. with user-guide.txt) can be | 132 | transition_latency * 100 |
137 | used to obtain exactly the same info: | 133 | Or by kernel restrictions: |
138 | show_sampling_rate_min = transtition_latency * 500 / 1000 | 134 | If CONFIG_NO_HZ is set, the limit is 10ms fixed. |
139 | show_sampling_rate_max = transtition_latency * 500000 / 1000 | 135 | If CONFIG_NO_HZ is not set or no_hz=off boot parameter is used, the |
140 | (divided by 1000 is to illustrate that sampling rate is in us and | 136 | limits depend on the CONFIG_HZ option: |
141 | transition latency is exported ns). | 137 | HZ=1000: min=20000us (20ms) |
138 | HZ=250: min=80000us (80ms) | ||
139 | HZ=100: min=200000us (200ms) | ||
140 | The highest value of kernel and HW latency restrictions is shown and | ||
141 | used as the minimum sampling rate. | ||
142 | |||
143 | show_sampling_rate_max: THIS INTERFACE IS DEPRECATED, DON'T USE IT. | ||
142 | 144 | ||
143 | up_threshold: defines what the average CPU usage between the samplings | 145 | up_threshold: defines what the average CPU usage between the samplings |
144 | of 'sampling_rate' needs to be for the kernel to make a decision on | 146 | of 'sampling_rate' needs to be for the kernel to make a decision on |