From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8F65C43381 for ; Wed, 20 Feb 2019 15:31:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9243420880 for ; Wed, 20 Feb 2019 15:31:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727591AbfBTPa7 (ORCPT ); Wed, 20 Feb 2019 10:30:59 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:39486 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725836AbfBTPa6 (ORCPT ); Wed, 20 Feb 2019 10:30:58 -0500 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1gwTpo-00079t-84; Wed, 20 Feb 2019 16:30:56 +0100 Date: Wed, 20 Feb 2019 16:30:56 +0100 From: Sebastian Andrzej Siewior To: Juri Lelli Cc: tglx@linutronix.de, linux-rt-users@vger.kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org, bristot@redhat.com, williams@redhat.com Subject: Re: [RFC PATCH RT 0/2] Add PINNED_HARD mode to hrtimers Message-ID: <20190220153055.dt7vm47c2auove3d@linutronix.de> References: <20190214133716.10187-1-juri.lelli@redhat.com> <20190219171905.qrpr5uurayfqbehp@linutronix.de> <20190220074751.GJ21785@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190220074751.GJ21785@localhost.localdomain> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-02-20 08:47:51 [+0100], Juri Lelli wrote: > > In this case you prepare the wakeup and then wake the CPU anyway. There > > should be no downside to this unless the housekeeping CPU is busy and in > > irq-off regions which would increase the latency. Also in case of > > cyclictest -d0 > > > > the one CPU would have to process all timers. So the latency will be > > worse compared to every CPU does its own wakeup. And on RT you probably > > do not want to do deep idle anyway. > > Mmm, right. But, still very much dependent on the workload, I understand > you are saying? So, no one size fits all solution. Now that I slept over it, I think it makes sense from RT point of view to always pin the timer. I'm not sure if we want to swap the sysctl or make the PINNED change like you suggested. > Thanks, > > - Juri Sebastian