Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753200AbbFXNoP (ORCPT ); Wed, 24 Jun 2015 09:44:15 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:51433 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752844AbbFXNoJ (ORCPT ); Wed, 24 Jun 2015 09:44:09 -0400 From: "Rafael J. Wysocki" To: Geert Uytterhoeven Cc: "Rafael J. Wysocki" , Ulf Hansson , Geert Uytterhoeven , Daniel Lezcano , Thomas Gleixner , Kevin Hilman , Magnus Damm , Laurent Pinchart , "linux-pm@vger.kernel.org" , Linux-sh list , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code Date: Wed, 24 Jun 2015 16:10:17 +0200 Message-ID: <10339007.ODJxqcfmHy@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.1.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: References: <1434622954-26747-3-git-send-email-geert+renesas@glider.be> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1976 Lines: 52 On Tuesday, June 23, 2015 03:45:43 PM Geert Uytterhoeven wrote: > Hi Rafael, > > On Tue, Jun 23, 2015 at 3:38 PM, Rafael J. Wysocki wrote: > >>>> @@ -2218,10 +2227,13 @@ int genpd_dev_pm_attach(struct device *dev) > >>>> > >>>> dev_dbg(dev, "adding to PM domain %s\n", pd->name); > >>>> > >>>> - while (1) { > >>>> + for (i = 0; i < GENPD_RETRIES; i++) { > >>>> ret = pm_genpd_add_device(pd, dev); > >>>> if (ret != -EAGAIN) > >>>> break; > >>>> + > >>>> + if (i > GENPD_RETRIES / 2) > >>>> + udelay(GENPD_DELAY_US); > >>> > >>> In this execution path, we retry when getting -EAGAIN while believing > >>> the reason to the error are only *temporary* as we are soon waiting > >>> for all devices in the genpd to be system PM resumed. At least that's > >>> my understanding to why we want to deal with -EAGAIN here, but I might > >>> be wrong. > >>> > >>> In this regards, I wonder whether it could be better to re-try only a > >>> few times but with a far longer interval time than a couple us. What > >>> do you think? > >> > >> That's indeed viable. I have no idea for how long this temporary state can > >> extend. > > > > A usual approach to this kind of thing is to use exponential fallback > > where you increase the delay twice with respect to the previous one > > every time. > > Right, but when do you give up? Well, I guess you know what a reasonable timeout should be? > Note that udelay() is a busy loop. Should it fall back to msleep() after > a while? If we can't fall back to msleep() at one point, you may as well simply poll periodically as you did originally. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/