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=-7.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS 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 97BBEC43381 for ; Mon, 25 Mar 2019 14:24:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 542912084D for ; Mon, 25 Mar 2019 14:24:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="NPybfnOj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729297AbfCYOYF (ORCPT ); Mon, 25 Mar 2019 10:24:05 -0400 Received: from mail-vk1-f193.google.com ([209.85.221.193]:34387 "EHLO mail-vk1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729204AbfCYOYE (ORCPT ); Mon, 25 Mar 2019 10:24:04 -0400 Received: by mail-vk1-f193.google.com with SMTP id k64so1985461vke.1 for ; Mon, 25 Mar 2019 07:24:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=18Uy2+5EeK7lK1NTsT1PhmlbcUQuf+mmQID+bLSg5mI=; b=NPybfnOjuYYvfG5P4rUPY46w6oJ+pu+1nvaFz3rSOexY5JI6jJwcZSiKwzUzZrsRsY mDrICkRcbzGwX0ct8NIYXBV7T+Bo79nVVBxs9FqkNnFVQpw5Cyuba/vuSA7L7nDuZbX+ Kc+cdGd8TZqVGpdAKVd5sXnWLHZQKoXU6WlR5ZCOM1zLrhaiqCpWq8FZxW1QfNqBZqGg gKpSVQqB31F/6nMY3yE8PpU2hRpDQcyYHYrX3CRasyrWnQjVNGseKCG17YqaZ762RKSt 44HsJWWbUK4Nxkhxo1NeDjSWziS5Mk7W6RV+zcH2PiYbhuGQGy130/18ZvicwrSkLWgj oPzw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=18Uy2+5EeK7lK1NTsT1PhmlbcUQuf+mmQID+bLSg5mI=; b=DEIvhHWrcko0qAB95nEP1zWjmr2mdNQtkEu62LSgNjdMQgsXFjAZRzPl22up3pCK+e EM9dVynx5hskWCFuMLOklQqXcleg+NkMWxR4jvv7UeMJD2zbAdAlXAKb1tQdp9QUByfY xpj6NFhv9K8HDlNewAn+6P8MMPPYchOx2It45ChbpG2/fvTUrkDWU+kCnd8xJ5As6kOO ftAJzCS/MUjkjtmVzXYiY/DeQFeLFkVNQh6jLJw7GZD79SLu2z+w4nfppzPLXU369Lr2 l8XXifEIOYSnLqN7KzeulKFuSWe4ia11m382wjN7fp1Y03bdFrMfzpg3RBNh+zsYS3Bz WrsQ== X-Gm-Message-State: APjAAAUKuMaGHV14XPvDNbAtDfs+Lbl6f36NRJ6QE60BRA6zDMP6jt+h D6lVTnC3cAONs269wS5TlPXELFhU8xGnDNZ9NrVmSA== X-Google-Smtp-Source: APXvYqyK5Sj8t0/bmtqkpbdMu8pleiBUSOsqzKm1/sXL0Xmus+qPMB2fDPyYUiHVAUaC20uNARhr/OqBhC599wkycao= X-Received: by 2002:a1f:3458:: with SMTP id b85mr3910490vka.4.1553523843044; Mon, 25 Mar 2019 07:24:03 -0700 (PDT) MIME-Version: 1.0 References: <20190227195836.24739-1-ulf.hansson@linaro.org> <20190227195836.24739-4-ulf.hansson@linaro.org> <2942111.nn8VVVUCAL@aspire.rjw.lan> In-Reply-To: <2942111.nn8VVVUCAL@aspire.rjw.lan> From: Ulf Hansson Date: Mon, 25 Mar 2019 15:23:27 +0100 Message-ID: Subject: Re: [PATCH v12 3/4] cpuidle: Export the next timer/tick expiration for a CPU To: "Rafael J. Wysocki" Cc: Linux PM , Frederic Weisbecker , Thomas Gleixner , Sudeep Holla , Lorenzo Pieralisi , Mark Rutland , Daniel Lezcano , "Raju P . L . S . S . S . N" , Stephen Boyd , Tony Lindgren , Kevin Hilman , Lina Iyer , Viresh Kumar , Vincent Guittot , Geert Uytterhoeven , Linux ARM , linux-arm-msm , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 25 Mar 2019 at 13:21, Rafael J. Wysocki wrote: > > On Wednesday, February 27, 2019 8:58:35 PM CET Ulf Hansson wrote: > > To be able to predict the sleep duration for a CPU that is entering idle, > > knowing when the next timer/tick is going to expire, is extremely useful. > > Both the teo and the menu cpuidle governors already makes use of this > > information, while selecting an idle state. > > > > Moving forward, the similar prediction needs to be done, but for a group of > > idle CPUs rather than for a single idle CPU. Following changes implements a > > new genpd governor, which needs this. > > > > Support this, by sharing a new function called > > tick_nohz_get_next_hrtimer(), which returns the next hrtimer or the next > > tick, whatever that expires first. > > > > Additionally, when cpuidle is about to invoke the ->enter() callback, then > > call tick_nohz_get_next_hrtimer() and store its return value in the per CPU > > struct cpuidle_device, as to make it available outside cpuidle. > > > > Do note, at the point when cpuidle calls tick_nohz_get_next_hrtimer(), the > > governor's ->select() callback has already made a decision whether to stop > > the tick or not. In this way, tick_nohz_get_next_hrtimer() actually returns > > the next timer expiration, whatever origin. > > > > Cc: Lina Iyer > > Co-developed-by: Lina Iyer > > Co-developed-by: Daniel Lezcano > > Signed-off-by: Ulf Hansson > > --- > > > > Changes in v12: > > - New patch. > > > > --- > > drivers/cpuidle/cpuidle.c | 8 ++++++++ > > include/linux/cpuidle.h | 1 + > > include/linux/tick.h | 7 ++++++- > > kernel/time/tick-sched.c | 12 ++++++++++++ > > 4 files changed, 27 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c > > index 7f108309e871..255365b1a6ab 100644 > > --- a/drivers/cpuidle/cpuidle.c > > +++ b/drivers/cpuidle/cpuidle.c > > @@ -328,6 +328,14 @@ int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, > > int cpuidle_enter(struct cpuidle_driver *drv, struct cpuidle_device *dev, > > int index) > > { > > + /* > > + * Store the next hrtimer, which becomes either next tick or the next > > + * timer event, whatever expires first. Additionally, to make this data > > + * useful for consumers outside cpuidle, we rely on that the governor's > > + * ->select() callback have decided, whether to stop the tick or not. > > + */ > > + dev->next_hrtimer = tick_nohz_get_next_hrtimer(); > > I would use WRITE_ONCE() to set next_hrtimer here and READ_ONCE() for > reading that value in the next patch, as a matter of annotation if > nothing else. Okay! > > > + > > if (cpuidle_state_is_coupled(drv, index)) > > return cpuidle_enter_state_coupled(dev, drv, index); > > return cpuidle_enter_state(dev, drv, index); > > Also I would clear next_hrtimer here to avoid dragging stale values > around. Right, I can do that. However, at least in my case it would be an unnecessary update of the variable, as I am never in a path where the value can be "stale". Even if one theoretically could use a stale value, it's seems likely to not be an issue, don't you think? Anyway, if I don't hear from you, I do the change as you suggested. > > Apart from this the series LGTM. Great, thanks. I re-spin a new version. Kind regards Uffe