On Thu, Aug 28, 2014 at 11:00:27AM +0100, Juri Lelli wrote: > Section 4 intro was still describing the old interface. Rewrite it. > > Signed-off-by: Juri Lelli <juri.lelli@xxxxxxx> > Signed-off-by: Luca Abeni <luca.abeni@xxxxxxxx> > Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Henrik Austad <henrik@xxxxxxxxx> > Cc: Dario Faggioli <raistlin@xxxxxxxx> > Cc: Juri Lelli <juri.lelli@xxxxxxxxx> > Cc: linux-doc@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > --- > Documentation/scheduler/sched-deadline.txt | 51 +++++++++++++++--------------- > 1 file changed, 25 insertions(+), 26 deletions(-) > > diff --git a/Documentation/scheduler/sched-deadline.txt b/Documentation/scheduler/sched-deadline.txt > index dce6d63..0aff2d5 100644 > --- a/Documentation/scheduler/sched-deadline.txt > +++ b/Documentation/scheduler/sched-deadline.txt > @@ -165,39 +165,38 @@ CONTENTS > > In order for the -deadline scheduling to be effective and useful, it is > important to have some method to keep the allocation of the available CPU > - bandwidth to the tasks under control. > - This is usually called "admission control" and if it is not performed at all, > - no guarantee can be given on the actual scheduling of the -deadline tasks. > - > - Since when RT-throttling has been introduced each task group has a bandwidth > - associated, calculated as a certain amount of runtime over a period. > - Moreover, to make it possible to manipulate such bandwidth, readable/writable > - controls have been added to both procfs (for system wide settings) and cgroupfs > - (for per-group settings). > - Therefore, the same interface is being used for controlling the bandwidth > - distrubution to -deadline tasks. > - > - However, more discussion is needed in order to figure out how we want to manage > - SCHED_DEADLINE bandwidth at the task group level. Therefore, SCHED_DEADLINE > - uses (for now) a less sophisticated, but actually very sensible, mechanism to > - ensure that a certain utilization cap is not overcome per each root_domain. > - > - Another main difference between deadline bandwidth management and RT-throttling > + bandwidth to the tasks under control. This is usually called "admission > + control" and if it is not performed at all, no guarantee can be given on > + the actual scheduling of the -deadline tasks. > + > + The interface used to control the fraction of CPU bandwidth that can be > + allocated to -deadline tasks is similar to the one already used for -rt > + tasks with real-time group scheduling (a.k.a. RT-throttling - see > + Documentation/scheduler/sched-rt-group.txt), and is based on readable/ > + writable control files located in procfs (for system wide settings). > + Notice that per-group settings (controlled through cgroupfs) are still not > + defined for -deadline tasks, because more discussion is needed in order to > + figure out how we want to manage SCHED_DEADLINE bandwidth at the task group > + level. > + > + A main difference between deadline bandwidth management and RT-throttling > is that -deadline tasks have bandwidth on their own (while -rt ones don't!), > - and thus we don't need an higher level throttling mechanism to enforce the > - desired bandwidth. > + and thus we don't need a higher level throttling mechanism to enforce the > + desired bandwidth. Therefore, using this simple interface we can put a cap > + on total utilization of -deadline tasks (i.e., \Sum (runtime_i / period_i) < > + some_desired_value). s/some_desired_value/global_dl_utilization_cap/ perhaps? > 4.1 System wide settings > ------------------------ > > The system wide settings are configured under the /proc virtual file system. > > - For now the -rt knobs are used for dl admission control and the -deadline > - runtime is accounted against the -rt runtime. We realise that this isn't > - entirely desirable; however, it is better to have a small interface for now, > - and be able to change it easily later. The ideal situation (see 5.) is to run > - -rt tasks from a -deadline server; in which case the -rt bandwidth is a direct > - subset of dl_bw. > + For now the -rt knobs are used for -deadline admission control and the > + -deadline runtime is accounted against the -rt runtime. We realise that this > + isn't entirely desirable; however, it is better to have a small interface for > + now, and be able to change it easily later. The ideal situation (see 5.) is to > + run -rt tasks from a -deadline server; in which case the -rt bandwidth is a > + direct subset of dl_bw. Isn't forking forbidden for _dl tasks? Or did I miss a memo somewhere? > This means that, for a root_domain comprising M CPUs, -deadline tasks > can be created while the sum of their bandwidths stays below: > -- > 2.0.4 > > All in all, looks pretty good to me! -- Henrik -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
