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Subject: Re: [RFD] sched/deadline: Support single CPU affinity
To: Peter Zijlstra <peterz@infradead.org>
References: <20161110080807.GD11311@worktop.programming.kicks-ass.net>
 <91d96936-7504-1578-d4e8-1f2f8d8dc113@sssup.it>
 <20161213102135.GJ3124@twins.programming.kicks-ass.net>
Cc: Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Juri Lelli <juri.lelli@gmail.com>, Luca Abeni <luca.abeni@unitn.it>,
        Steven Rostedt <rostedt@goodmis.org>,
        Claudio Scordino <claudio@evidence.eu.com>,
        Daniel Bistrot de Oliveira <danielbristot@gmail.com>,
        Henrik Austad <henrik@austad.us>, linux-kernel@vger.kernel.org
From: Tommaso Cucinotta <tommaso.cucinotta@sssup.it>
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Date: Thu, 15 Dec 2016 12:30:43 +0100
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Hi Peter,

On 13/12/2016 11:21, Peter Zijlstra wrote:
> On Thu, Nov 10, 2016 at 11:01:59AM +0100, Tommaso Cucinotta wrote:
>> Just a note: if you want to recover arbitrary task affinities, you can re-cast your above test like this:
>>
>> for_each_processor(cpu)
>>    \sum U[t]/A[t] \leq 1 (or U_max), for each task t on cpu, with utilization U[t] and A[t] tasks overall in its affinity mask
>>
> Do I read it correct when I interpret A[t] as the number of CPUs in its
> affinity mask?

yes, exactly, A[t] number of CPUs in the task affinity mask (sorry for my bad write-up)

> Also, does recoverable mean a bound tardiness, or is that something
> weaker still?

nope, nothing exact -- it just meant providing flexible but simple & consistent (ie, towards recovering affinity masks) options from the kernel/scheduler side, leaving more complex & exact tests to user-space, or future add-ons to the kernel.

Thanks,

     T.