From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752600AbdKFMKH (ORCPT ); Mon, 6 Nov 2017 07:10:07 -0500 Received: from mail-it0-f67.google.com ([209.85.214.67]:51986 "EHLO mail-it0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752296AbdKFMKF (ORCPT ); Mon, 6 Nov 2017 07:10:05 -0500 X-Google-Smtp-Source: ABhQp+Q5oPqAUFR/bOB+FJXgxxIs9DJAz4fSAaglkb3Ws9as4jEFRidXQ8JzatB7yADMFFgE4UUi4EKXiFn12Rem53Y= MIME-Version: 1.0 In-Reply-To: <1780873.Ca3tjQj9XB@aspire.rjw.lan> References: <5770848.Kdi5IjVKeE@aspire.rjw.lan> <2520927.XkLgALY3I0@aspire.rjw.lan> <1780873.Ca3tjQj9XB@aspire.rjw.lan> From: Ulf Hansson Date: Mon, 6 Nov 2017 13:10:03 +0100 Message-ID: Subject: Re: [RFT][PATCH v2 1/2] PM / domains: Rework governor code to be more consistent To: "Rafael J. Wysocki" Cc: Linux PM , LKML , Geert Uytterhoeven , Tero Kristo , Reinette Chatre , Ramesh Thomas , Alex Shi Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3 November 2017 at 12:47, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki > > The genpd governor currently uses negative PM QoS values to indicate > the "no suspend" condition and 0 as "no restriction", but it doesn't > use them consistently. Moreover, it tries to refresh QoS values for > already suspended devices in a quite questionable way. > > For the above reasons, rework it to be a bit more consistent. > > First off, note that dev_pm_qos_read_value() in > dev_update_qos_constraint() and __default_power_down_ok() is > evaluated for devices in suspend. Moreover, that only happens if the > effective_constraint_ns value for them is negative (meaning "no > suspend"). It is not evaluated in any other cases, so effectively > the QoS values are only updated for devices in suspend that should > not have been suspended in the first place. In all of the other > cases, the QoS values taken into account are the effective ones from > the time before the device has been suspended, so generally devices > need to be resumed and suspended again for new QoS values to take > effect anyway. Thus evaluating dev_update_qos_constraint() in > those two places doesn't make sense at all, so drop it. > > Second, initialize effective_constraint_ns to 0 ("no constraint") > rather than to (-1) ("no suspend"), which makes more sense in > general and in case effective_constraint_ns is never updated > (the device is in suspend all the time or it is never suspended) > it doesn't affect the device's parent and so on. > > Finally, rework default_suspend_ok() to explicitly handle the > "no restriction" special case. > > Signed-off-by: Rafael J. Wysocki > --- > drivers/base/power/domain.c | 2 - > drivers/base/power/domain_governor.c | 61 +++++++++++++++++++++-------------- > 2 files changed, 38 insertions(+), 25 deletions(-) > > Index: linux-pm/drivers/base/power/domain.c > =================================================================== > --- linux-pm.orig/drivers/base/power/domain.c > +++ linux-pm/drivers/base/power/domain.c > @@ -1331,7 +1331,7 @@ static struct generic_pm_domain_data *ge > > gpd_data->base.dev = dev; > gpd_data->td.constraint_changed = true; > - gpd_data->td.effective_constraint_ns = -1; > + gpd_data->td.effective_constraint_ns = 0; > gpd_data->nb.notifier_call = genpd_dev_pm_qos_notifier; > > spin_lock_irq(&dev->power.lock); > Index: linux-pm/drivers/base/power/domain_governor.c > =================================================================== > --- linux-pm.orig/drivers/base/power/domain_governor.c > +++ linux-pm/drivers/base/power/domain_governor.c > @@ -14,22 +14,22 @@ > static int dev_update_qos_constraint(struct device *dev, void *data) > { > s64 *constraint_ns_p = data; > - s32 constraint_ns = -1; > - > - if (dev->power.subsys_data && dev->power.subsys_data->domain_data) > - constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns; > + s64 constraint_ns; > > - if (constraint_ns < 0) { > - constraint_ns = dev_pm_qos_read_value(dev); > - constraint_ns *= NSEC_PER_USEC; > - } > - if (constraint_ns == 0) > + if (!dev->power.subsys_data || !dev->power.subsys_data->domain_data) > return 0; > > /* > - * constraint_ns cannot be negative here, because the device has been > - * suspended. > + * Only take suspend-time QoS constraints of devices into account, > + * because constraints updated after the device has been suspended are > + * not guaranteed to be taken into account anyway. In order for them > + * to take effect, the device has to be resumed and suspended again. > */ This means a change in behavior, because earlier we took into account QoS values for child devices that were not attached to a genpd. Is there any reason you think we should change this, or is it just something you overlooked here? I understand, that if the QoS constraint has been updated after such child device has been suspended, it's tricky to take a correct decision. To really solve this, we would either have to register a QoS notifier for all children devices that has its parent attached to a genpd, or always runtime resume devices before updating QoS constraints. Non of these options is perfect, so perhaps we should consider a "best effort" approach instead? Whatever that may be. > + constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns; > + /* 0 means "no constraint" */ > + if (constraint_ns == 0) > + return 0; > + > if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0) > *constraint_ns_p = constraint_ns; > > @@ -76,14 +76,29 @@ static bool default_suspend_ok(struct de > device_for_each_child(dev, &constraint_ns, > dev_update_qos_constraint); > > - if (constraint_ns > 0) { > + if (constraint_ns == 0) { > + /* "No restriction", so the device is allowed to suspend. */ > + td->effective_constraint_ns = 0; > + td->cached_suspend_ok = true; > + } else { > + /* > + * constraint_ns must be positive here, because the children > + * walked above are all suspended, so effective_constraint_ns > + * cannot be negative for them. > + */ > constraint_ns -= td->suspend_latency_ns + > td->resume_latency_ns; > - if (constraint_ns == 0) > + /* > + * effective_constraint_ns is negative already and > + * cached_suspend_ok is false, so if the computed value is not > + * positive, return right away. > + */ > + if (constraint_ns <= 0) > return false; > + > + td->effective_constraint_ns = constraint_ns; > + td->cached_suspend_ok = true; > } > - td->effective_constraint_ns = constraint_ns; > - td->cached_suspend_ok = constraint_ns >= 0; > > /* > * The children have been suspended already, so we don't need to take > @@ -144,18 +159,16 @@ static bool __default_power_down_ok(stru > */ > td = &to_gpd_data(pdd)->td; > constraint_ns = td->effective_constraint_ns; > - /* default_suspend_ok() need not be called before us. */ > - if (constraint_ns < 0) { > - constraint_ns = dev_pm_qos_read_value(pdd->dev); > - constraint_ns *= NSEC_PER_USEC; > - } > + /* > + * Negative values mean "no suspend at all" and this runs only > + * when all devices in the domain are suspended, so it must be > + * 0 at least. > + * > + * 0 means "no constraint" > + */ > if (constraint_ns == 0) > continue; > > - /* > - * constraint_ns cannot be negative here, because the device has > - * been suspended. > - */ > if (constraint_ns <= off_on_time_ns) > return false; > > Kind regards Uffe