On 04/30/20 13:06, Tao Zhou wrote: > Hi, > > On Tue, Apr 28, 2020 at 05:41:34PM +0100, Qais Yousef wrote: > > 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 > > --- > > Documentation/admin-guide/sysctl/kernel.rst | 48 +++++++++++++++++++++ > > 1 file changed, 48 insertions(+) > > > > diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst > > index 0d427fd10941..e7255f71493c 100644 > > --- a/Documentation/admin-guide/sysctl/kernel.rst > > +++ b/Documentation/admin-guide/sysctl/kernel.rst > > @@ -940,6 +940,54 @@ 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 > ^^^^^^^ > > Seems that 'greater' should be 'smaller'. > And the range is [sched_util_clamp_min:SCHED_CAPACITY_SCALE] > Uclamp request should not below this system value. > Or I am totally wrong for memory leak. No the range is [0:sched_util_clamp_min]. It is what it is implemented by this condition: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/sched/core.c?h=v5.7-rc3#n913 So if the requested uclamp.min value is greater than sched_util_clamp_min, we return sched_util_clamp_min. Thanks -- Qais Yousef > > Thank you > > > +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_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 > > +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 opportunity the scheduler needs > > +to calculate the effective value of uclamp.min of the task. > > > > seccomp > > ======= > > -- > > 2.17.1 > >
