linux-kernel - Re: [RFD] sched/deadline: Support single CPU affinity

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Message-ID: <20161213102135.GJ3124@twins.programming.kicks-ass.net>
Date:   Tue, 13 Dec 2016 11:21:35 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tommaso Cucinotta <tommaso.cucinotta@...up.it>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juri Lelli <juri.lelli@...il.com>,
        Luca Abeni <luca.abeni@...tn.it>,
        Steven Rostedt <rostedt@...dmis.org>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Daniel Bistrot de Oliveira <danielbristot@...il.com>,
        Henrik Austad <henrik@...tad.us>, linux-kernel@...r.kernel.org
Subject: Re: [RFD] sched/deadline: Support single CPU affinity

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?

For A[t] == 1, that reduces to the UP case:

	\Sum U[t] \leq 1

and A[t] = N that reduces to the G-EDF case:

	\Sum U[t] \leq N


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