linux-kernel - Re: [PATCH 4/5] sched/isolation: Residual 1Hz scheduler tick offload

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Date:   Tue, 19 Dec 2017 17:04:57 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Wanpeng Li <kernellwp@...il.com>,
        Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 4/5] sched/isolation: Residual 1Hz scheduler tick offload

On Tue, Dec 19, 2017 at 10:01:46AM -0600, Christopher Lameter wrote:
> On Tue, 19 Dec 2017, Peter Zijlstra wrote:
> 
> > On Tue, Dec 19, 2017 at 04:23:57AM +0100, Frederic Weisbecker wrote:
> > > When a CPU runs in full dynticks mode, a 1Hz tick remains in order to
> > > keep the scheduler stats alive. However this residual tick is a burden
> > > for Real-Time tasks that can't stand no interruption at all.
> >
> > I'm not sure that is accurate. RT doesn't necessarily have anything much
> > to so with this. The tick is per definition very deterministic and thus
> > should not be a problem.
> 
> Depends what one means by RT. 

Real Time computing as per the literature. Any other definition is
wrong and confusing.