Uclamp exposes 3 sysctl knobs: * sched_util_clamp_min * sched_util_clamp_max * sched_rt_default_util_clamp_min 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 --- Documentation/admin-guide/sysctl/kernel.rst | 47 +++++++++++++++++++++ 1 file changed, 47 insertions(+) diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index def074807cee..5e974cd493b5 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -935,6 +935,53 @@ 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 SCHED_CAPACITY_SCALE (1024), which is the maximum possible +value. + +It means that any requested uclamp.min value cannot be greater than +sched_util_clamp_min, ie: it is restricted to the range +[0:sched_util_clamp_min]. + +sched_util_clamp_max: +===================== + +Max allowed *maximum* utilization. + +Default value is SCHED_CAPACITY_SCALE (1024), which is the maximum possible +value. + +It means that any requested uclamp.max value cannot be greater than +sched_util_clamp_max, ie: it is restricted to the range +[0:sched_util_clamp_max]. + +sched_rt_default_util_clamp_min: +================================ + +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 +hetergenous systems). + +Uclamp achieves this by setting the requested uclamp.min of all RT tasks to +SCHED_CAPACITY_SCALE (1024) by default. Which effectively boosts the tasks to +run at the highest frequency and bias 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 constraint imposed by sched_util_clamp_min +defined above. + +Any modification is applied lazily on the next RT task wakeup. sg-big-buff: ============ -- 2.17.1
