linux-kernel - Re: [RFD] sched/deadline: EDF dynamic quota design

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Date:	Tue, 17 Jun 2014 10:01:22 +0200
From:	Luca Abeni <luca.abeni@...tn.it>
To:	"xiaofeng.yan" <xiaofeng.yan@...wei.com>
CC:	Henrik Austad <henrik@...tad.us>,
	Juri Lelli <juri.lelli@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, duzhiping.du@...wei.com,
	xiaofeng.yan2012@...il.com, raistlin@...ux.it, tkhai@...dex.ru,
	harald.gustafsson@...csson.com, linux-kernel@...r.kernel.org
Subject: Re: [RFD] sched/deadline: EDF dynamic quota design

Hi,

On 06/17/2014 04:43 AM, xiaofeng.yan wrote:
[...]
>> The basic ideas are (warning! This is an over-simplification of the algorithm! :)
>> - You assign runtime and period to each SCHED_DEADLINE task as usual
>> - Each task is guaranteed to receive its runtime every period
>> - You can also define a maximum fraction Umax of the CPU time that the
>>   SCHED_DEADLINE tasks can use. Note that Umax _must_ be larger or equal
>>   than sum_i runtime_i / period_i
>>   (note: in the original GRUB paper, only one CPU is considered, and Umax is
>>   set equal to 1)
>> - If the tasks are consuming less than Umax, then the scheduling algorithm
>>   allows them to use more runtime (but not less than the guaranteed runtime_i)
>>   in order to use up to Umax.
>>   This is achieved by modifying the rule used to decrease the runtime: in
>>   SCHED_DEADLINE, if a task executes for a time delta, its runtime is decreased
>>   by delta; using GRUB, it would be decreased by a smaller amount of time
>>   (computed based on Umax, on the active SCHED_DEADLINE tasks, etc...).
>>   This requires to implement some kind of state machine (the details are in
>>   the GRUB paper)
>>
>> I also had an implementation of the GRUB algorithm (based on a modification
>> of my old CBS scheduler for Linux), but the computational complexity of the
>> algorithm was too high. That's why I never proposed to merge it in SCHED_DEADLINE.
>> But maybe there can be some trade-off between the "exact compliance with the
>> GRUB algorithm" and implementation efficiency that can make it acceptable...
>>
>>
> Has these  codes been opened about the implementation in some community or not ?
The old GRUB scheduler for Linux was used for some experiments published in a paper
at RTLWS 2007, and of course the code was open-source (released under GPL).
It required a patch for the Linux kernel (I used a 2.6.something kernel) which allowed
to load the scheduler as a kernel module (yes, I know this is the wrong way to go...
But implementing it like this was simpler :).
That is very old code... I probably still have it somewhere, but I have to search
for it. If someone is interested, I can try to search (the story of the user-space
daemon for adaptive reservations is similar: I released it as open-source years ago...
If anyone is interested I can search for this code too)


				Luca
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