linux-kernel - Re: [RFC 7/8] Make GRUB a task's flag

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Date:	Fri, 15 Jan 2016 09:15:39 +0100
From:	Luca Abeni <luca.abeni@...tn.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@....com>
Subject: Re: [RFC 7/8] Make GRUB a task's flag

On 01/14/2016 08:56 PM, Peter Zijlstra wrote:
> On Thu, Jan 14, 2016 at 04:24:52PM +0100, Luca Abeni wrote:
>> +++ b/include/uapi/linux/sched.h
>> @@ -48,5 +48,6 @@
>>    * For the sched_{set,get}attr() calls
>>    */
>>   #define SCHED_FLAG_RESET_ON_FORK	0x01
>> +#define SCHED_FLAG_RECLAIM		0x02
>
> With an eye towards unpriv usage of SCHED_DEADLINE, this isn't something
> we could allow unpriv tasks, right? Since (IIRC) GRUB will allow eating
> all !deadline time.
The original algorithm, yes, it allowed to use 100% of the CPU time, starving
all !deadline tasks.
But in this patchset I modified the algorithm to allow reclaiming only a
fraction U_max of the CPU time... So, 1-U_max can be left free for !deadline.


> Something with an average runtime/budget that also puts limits on the
> max (say 2*avg) would be far more amenable to be exposed to unpriv
> tasks, except since that would directly result in an average tardiness
> bound this might be non-trivial to combine with tasks not opting for
> this.
I'll try to think about this... The advantage of GRUB is that a theoretically
sound algorithm already existed; here, we would need to design the algorithm
so that it does not break the SCHED_DEADLINE guarantees. Anyway, this is an
interesting challenge, I'll work on it :)



			Thanks,
				Luca