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

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Message-ID: <20171219093435.43c863a3@redhat.com>
Date:   Tue, 19 Dec 2017 09:34:35 -0500
From:   Luiz Capitulino <lcapitulino@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Lameter <cl@...ux.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, 19 Dec 2017 10:19:11 +0100
Peter Zijlstra <peterz@...radead.org> 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.

What Frederic says is certainly true for HPC. But even for RT I'd say
this is a very nice feature, since it may reduce maximum latency.