From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754822AbbFWNpt (ORCPT ); Tue, 23 Jun 2015 09:45:49 -0400 Received: from mail-oi0-f44.google.com ([209.85.218.44]:33425 "EHLO mail-oi0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754585AbbFWNpo (ORCPT ); Tue, 23 Jun 2015 09:45:44 -0400 MIME-Version: 1.0 In-Reply-To: References: <1434622954-26747-3-git-send-email-geert+renesas@glider.be> <1434958282-27376-1-git-send-email-geert+renesas@glider.be> Date: Tue, 23 Jun 2015 15:45:43 +0200 X-Google-Sender-Auth: Vaq5W83qWT32d9y7H62Ju_t3hZk Message-ID: Subject: Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code From: Geert Uytterhoeven To: "Rafael J. Wysocki" Cc: Ulf Hansson , Geert Uytterhoeven , Daniel Lezcano , Thomas Gleixner , "Rafael J. Wysocki" , Kevin Hilman , Magnus Damm , Laurent Pinchart , "linux-pm@vger.kernel.org" , Linux-sh list , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Note that udelay() is a busy loop. Should it fall back to msleep() after a while? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds From mboxrd@z Thu Jan 1 00:00:00 1970 From: Geert Uytterhoeven Date: Tue, 23 Jun 2015 13:45:43 +0000 Subject: Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code Message-Id: List-Id: References: <1434622954-26747-3-git-send-email-geert+renesas@glider.be> In-Reply-To: <1434622954-26747-3-git-send-email-geert+renesas@glider.be> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-sh@vger.kernel.org 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? Note that udelay() is a busy loop. Should it fall back to msleep() after a while? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds