Uclamp exposes 3 sysctl knobs: * sched_util_clamp_min * sched_util_clamp_max * sched_util_clamp_min_rt_default Document them in sysctl/kernel.rst. Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx> CC: Jonathan Corbet <corbet@xxxxxxx> CC: Juri Lelli <juri.lelli@xxxxxxxxxx> CC: Vincent Guittot <vincent.guittot@xxxxxxxxxx> CC: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> CC: Steven Rostedt <rostedt@xxxxxxxxxxx> CC: Ben Segall <bsegall@xxxxxxxxxx> CC: Mel Gorman <mgorman@xxxxxxx> CC: Luis Chamberlain <mcgrof@xxxxxxxxxx> CC: Kees Cook <keescook@xxxxxxxxxxxx> CC: Iurii Zaikin <yzaikin@xxxxxxxxxx> CC: Quentin Perret <qperret@xxxxxxxxxx> CC: Valentin Schneider <valentin.schneider@xxxxxxx> CC: Patrick Bellasi <patrick.bellasi@xxxxxxxxxx> CC: Pavan Kondeti <pkondeti@xxxxxxxxxxxxxx> CC: linux-doc@xxxxxxxxxxxxxxx CC: linux-kernel@xxxxxxxxxxxxxxx CC: linux-fsdevel@xxxxxxxxxxxxxxx --- Changes in v5: * Improve the wording about the lazy update and the relationship to sched_util_clamp_min (Patrick) Documentation/admin-guide/sysctl/kernel.rst | 57 +++++++++++++++++++++ 1 file changed, 57 insertions(+) diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index 0d427fd10941..6cd3cb0e22c0 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -940,6 +940,63 @@ Enables/disables scheduler statistics. Enabling this feature incurs a small amount of overhead in the scheduler but is useful for debugging and performance tuning. +sched_util_clamp_min: +===================== + +Max allowed *minimum* utilization. + +Default value is 1024, which is the maximum possible value. + +It means that any requested uclamp.min value cannot be greater than +sched_util_clamp_min, i.e., it is restricted to the range +[0:sched_util_clamp_min]. + +sched_util_clamp_max: +===================== + +Max allowed *maximum* utilization. + +Default value is 1024, which is the maximum possible value. + +It means that any requested uclamp.max value cannot be greater than +sched_util_clamp_max, i.e., it is restricted to the range +[0:sched_util_clamp_max]. + +sched_util_clamp_min_rt_default: +================================ + +By default Linux is tuned for performance. Which means that RT tasks always run +at the highest frequency and most capable (highest capacity) CPU (in +heterogeneous systems). + +Uclamp achieves this by setting the requested uclamp.min of all RT tasks to +1024 by default, which effectively boosts the tasks to run at the highest +frequency and biases them to run on the biggest CPU. + +This knob allows admins to change the default behavior when uclamp is being +used. In battery powered devices particularly, running at the maximum +capacity and frequency will increase energy consumption and shorten the battery +life. + +This knob is only effective for RT tasks which the user hasn't modified their +requested uclamp.min value via sched_setattr() syscall. + +This knob will not escape the range constraint imposed by sched_util_clamp_min +defined above. + +For example if + + sched_util_clamp_min_rt_default = 800 + sched_util_clamp_min = 600 + +Then the boost will be clamped to 600 because 800 is outside of the permissible +range of [0:600]. This could happen for instance if a powersave mode will +restrict all boosts temporarily by modifying sched_util_clamp_min. As soon as +this restriction is lifted, the requested sched_util_clamp_min_rt_default +will take effect. + +Any modification is applied lazily to tasks and is effective starting from +their next wakeup. seccomp ======= -- 2.17.1
