linux-kernel - Re: [PATCH v2 3/4] Documentation/scheduler/sched-deadline.txt: improve and clarify AC bits

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Message-ID: <20140822083110.GB8771@gmail.com>
Date:	Fri, 22 Aug 2014 10:31:11 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Luca Abeni <luca.abeni@...tn.it>
Cc:	Juri Lelli <juri.lelli@....com>, peterz@...radead.org,
	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 3/4] Documentation/scheduler/sched-deadline.txt:
 improve and clarify AC bits


* Luca Abeni <luca.abeni@...tn.it> wrote:

> Hi Ingo,
> 
> On Thu, 21 Aug 2014 15:38:37 +0200
> Ingo Molnar <mingo@...nel.org> wrote:
> [...]
> > > + If the total utilisation sum_i(WCET_i/P_i) (sum of the
> > > utilisations
> > > + WCET_i/P_i of all the tasks in the system - notice that when
> > > considering
> > > + multiple tasks, the parameters of the i-th one are indicated with
> > > the "_i"
> > > + suffix) is larger than M (with M equal to the number of CPUs),
> > > then the
> > > + system will surely not be able to respect all of the deadlines,
> > > and no
> > > + execution time is guaranteed for non real-time tasks, which risk
> > > to be
> > > + starved by real-time tasks.
> > 
> > The last part doesn't really parse as correct English for me - 
> > maybe also split this overly long sentence into two or three 
> > sentences, to make it easier to understand?
> Sorry about this; after re-reading the sentence, I agree it looks
> confusing. What about:

Looks good to me, with a few details:

> "
> If the total utilisation sum_i(WCET_i/P_i) is larger than M (with M
> equal to the number of CPUs), then the scheduler can not be able to
> respect all of the deadlines.

s/can not be able to respect/is unable to respect

> Note that the total utilisation is defined as the sum of the
> utilisations WCET_i/P_i of all the real-time tasks in the system (when
> considering multiple real-time tasks, the parameters of the i-th one are
> indicated with the "_i" suffix).

The parentheses are a bit confusing here - they come after a 
half finished sentence - which at the end turns out to have 
ended.

How about something like:

> Note that total utilisation is defined as the sum of the 
> utilisations WCET_i/P_i over all the real-time tasks in the 
> system. When considering multiple real-time tasks, the 
> parameters of the i-th task are indicated with the "_i" 
> suffix.

?

> Moreover, if the total utilisation is larger than M, then non real-time
> tasks risk to be starved by real-time tasks.

How about:

> Moreover, if the total utilisation is larger than M, then we 
> risk starving non- real-time tasks by real-time tasks.

?

Thanks,

	Ingo
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