linux-kernel - Re: [RFC PATCH v2 6/6] sched/fair: Implement starvation monitor

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Message-ID: <20200807134353.GR42956@localhost.localdomain>
Date:   Fri, 7 Aug 2020 15:43:53 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     luca abeni <luca.abeni@...tannapisa.it>
Cc:     peterz@...radead.org, mingo@...hat.com, rostedt@...dmis.org,
        tglx@...utronix.de, linux-kernel@...r.kernel.org,
        tommaso.cucinotta@...tannapisa.it, alessio.balsini@...il.com,
        bristot@...hat.com, dietmar.eggemann@....com,
        linux-rt-users@...r.kernel.org, mtosatti@...hat.com,
        williams@...hat.com, valentin.schneider@....com
Subject: Re: [RFC PATCH v2 6/6] sched/fair: Implement starvation monitor

On 07/08/20 15:28, luca abeni wrote:
> Hi Juri,
> 
> On Fri, 7 Aug 2020 11:56:04 +0200
> Juri Lelli <juri.lelli@...hat.com> wrote:
> 
> > Starting deadline server for lower priority classes right away when
> > first task is enqueued might break guarantees
> 
> Which guarantees are you thinking about, here? Response times of fixed
> priority tasks?

Response time, but also wakeup latency (which, for better or worse, is
another important metric).

> If fixed priority tasks are also scheduled through deadline servers,
> then you can provide response-time guarantees to them even when
> lower-priority/non-real-time tasks are scheduled through deadline
> servers.

Right, but I fear we won't be able to keep current behavior for wakeups:
RT with highest prio always gets scheduled right away?