Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763538AbdLSOem (ORCPT ); Tue, 19 Dec 2017 09:34:42 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55680 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763488AbdLSOek (ORCPT ); Tue, 19 Dec 2017 09:34:40 -0500 Date: Tue, 19 Dec 2017 09:34:35 -0500 From: Luiz Capitulino To: Peter Zijlstra Cc: Frederic Weisbecker , LKML , Chris Metcalf , Thomas Gleixner , Christoph Lameter , "Paul E . McKenney" , Ingo Molnar , Wanpeng Li , Mike Galbraith , Rik van Riel Subject: Re: [PATCH 4/5] sched/isolation: Residual 1Hz scheduler tick offload Message-ID: <20171219093435.43c863a3@redhat.com> In-Reply-To: <20171219091911.tg2k4w7mgv2bcmeb@hirez.programming.kicks-ass.net> References: <1513653838-31314-1-git-send-email-frederic@kernel.org> <1513653838-31314-5-git-send-email-frederic@kernel.org> <20171219091911.tg2k4w7mgv2bcmeb@hirez.programming.kicks-ass.net> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Tue, 19 Dec 2017 14:34:40 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 684 Lines: 14 On Tue, 19 Dec 2017 10:19:11 +0100 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. 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.