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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 278F8C43381 for ; Wed, 20 Feb 2019 07:48:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0258E2183F for ; Wed, 20 Feb 2019 07:48:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726017AbfBTHsB (ORCPT ); Wed, 20 Feb 2019 02:48:01 -0500 Received: from mail-wm1-f68.google.com ([209.85.128.68]:54155 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725819AbfBTHsB (ORCPT ); Wed, 20 Feb 2019 02:48:01 -0500 Received: by mail-wm1-f68.google.com with SMTP id e74so4915226wmg.3 for ; Tue, 19 Feb 2019 23:48:00 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=mMMDihoOxx8auqqxwzKnxdWtX+ynPEcI5yhKxVPfzYo=; b=MUIf2/Wxqe94cosFbVC4DHF7mj9s6YJYrRqfWL2hE58lLUNvboYNoTtdVliQ30jhiD 3wBps20ZVw341cuNrIPhDIEkFwcD4dN5A5a4QfPoSfhr5NRh/3dsi0FYIF0dJDWiH6v8 3Ro6QzBR7BlnVoX4oL2ftw7ox/5w/nnKFehxO5jSvmfd6Wpjge7gJk6NkABG0UChkxa9 kt2gk7opeXQXNX7PAEraZL/K9yOypYraJtaIpcac5lxa6OBysA4Ls0fTOo8y/zc21Maz ARhUsa41bXg+ZLM65xf+xE9FNfRlNAwqCpWyAPpDChrphHTKwsXHrQYF9u396IA5My9G l3Sg== X-Gm-Message-State: AHQUAubCb0N1KOH6nayDGQqJq+BBZCoarL7bodw9N1I1GwwO3PiWTBo8 RafOgjfd5JFtm0PMbtfKf9vuDg== X-Google-Smtp-Source: AHgI3IZjZXb91A+ELotyzyyE9XSLRWoy0E+Av7CAPVM29BAQmPs+eSO7MA1lPKE4ukl6rd9oMEhdhw== X-Received: by 2002:a1c:1c4:: with SMTP id 187mr5927055wmb.6.1550648879392; Tue, 19 Feb 2019 23:47:59 -0800 (PST) Received: from localhost.localdomain ([151.15.254.225]) by smtp.gmail.com with ESMTPSA id b3sm9962891wme.27.2019.02.19.23.47.58 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 19 Feb 2019 23:47:58 -0800 (PST) Date: Wed, 20 Feb 2019 08:47:51 +0100 From: Juri Lelli To: Sebastian Andrzej Siewior 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: <20190220074751.GJ21785@localhost.localdomain> References: <20190214133716.10187-1-juri.lelli@redhat.com> <20190219171905.qrpr5uurayfqbehp@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190219171905.qrpr5uurayfqbehp@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/02/19 18:19, Sebastian Andrzej Siewior wrote: > On 2019-02-14 14:37:14 [+0100], Juri Lelli wrote: > > Hi, > Hi, > > > Now, I'm sending this and an RFC, as I'm wondering if the first behavior > > is actually what we want, and it is not odd at all for reasons that are > > not evident to me at the moment. In this case this posting might also > > function as a question: why we need things to work as they are today? > > There is /proc/sys/kernel/timer_migration which should disable this but > I think you know that already. > > So this is a NO_HZ feature. Basically try to move all the timers to a > designated CPU so all others can deep idle while one CPU does the work. > Ideally you have no timer which is pending / will expire if you go idle. > And then, once the timer fires the housekeeping CPU does the work so > chances are that the CPU, that programmed the timer, may remain idle. Right. > 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. Thanks, - Juri