linux-kernel - Re: [PATCH v2 2/4] Documentation/scheduler/sched-deadline.txt: Rewrite section 4 intro

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Date:	Thu, 21 Aug 2014 15:46:25 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Juri Lelli <juri.lelli@....com>
Cc:	peterz@...radead.org, luca.abeni@...tn.it, rdunlap@...radead.org,
	mingo@...hat.com, henrik@...tad.us, raistlin@...ux.it,
	juri.lelli@...il.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] Documentation/scheduler/sched-deadline.txt:
 Rewrite section 4 intro

* Juri Lelli <juri.lelli@....com> wrote:

> Section 4 intro was still describing the old interface. Rewrite it.
> 
> Signed-off-by: Juri Lelli <juri.lelli@....com>
> Signed-off-by: Luca Abeni <luca.abeni@...tn.it>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Henrik Austad <henrik@...tad.us>
> Cc: Dario Faggioli <raistlin@...ux.it>
> Cc: Juri Lelli <juri.lelli@...il.com>
> Cc: linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  Documentation/scheduler/sched-deadline.txt | 49 +++++++++++++++---------------
>  1 file changed, 24 insertions(+), 25 deletions(-)
> 
> diff --git a/Documentation/scheduler/sched-deadline.txt b/Documentation/scheduler/sched-deadline.txt
> index dce6d63..8372c3d 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

s/an higher/a higher

> - desired bandwidth.
> + desired bandwidth. Therefore, using this simple interface, we can put a cap

s/interface, we/interface we

> + on total utilization of -deadline tasks (i.e., \Sum (runtime_i / period_i) <
> + some_desired_value).

Thanks,

	Ingo

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