From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752667AbdKGFMd (ORCPT ); Tue, 7 Nov 2017 00:12:33 -0500 Received: from mga04.intel.com ([192.55.52.120]:3322 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752580AbdKGFMb (ORCPT ); Tue, 7 Nov 2017 00:12:31 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,356,1505804400"; d="scan'208";a="4318965" Date: Mon, 6 Nov 2017 21:05:45 -0800 From: Ramesh Thomas To: "Rafael J. Wysocki" Cc: Linux PM , LKML , Ulf Hansson , Geert Uytterhoeven , Tero Kristo , Reinette Chatre , Alex Shi Subject: Re: [PATCH v3 1/2] PM / domains: Rework governor code to be more consistent Message-ID: <20171107050544.GB17606@intel.com> Reply-To: ramesh.thomas@intel.com References: <5770848.Kdi5IjVKeE@aspire.rjw.lan> <2520927.XkLgALY3I0@aspire.rjw.lan> <2941273.uOhv3ydaDP@aspire.rjw.lan> <3615978.1OBBRZE5lx@aspire.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3615978.1OBBRZE5lx@aspire.rjw.lan> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017-11-07 at 02:23:18 +0100, 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" and "no suspend" special cases. > > Also add WARN_ON() around checks that should never trigger. > > Signed-off-by: Rafael J. Wysocki > Tested-by: Geert Uytterhoeven > --- > > v2 -> v3: Take children that don't belong to genpd power domains into > account in dev_update_qos_constraint(). > > --- > drivers/base/power/domain.c | 2 > drivers/base/power/domain_governor.c | 71 ++++++++++++++++++++++++----------- > 2 files changed, 50 insertions(+), 23 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 +14,33 @@ > static int dev_update_qos_constraint(struct device *dev, void *data) > { > s64 *constraint_ns_p = data; > - s32 constraint_ns = -1; > + s64 constraint_ns; > > - if (dev->power.subsys_data && dev->power.subsys_data->domain_data) > + if (dev->power.subsys_data && dev->power.subsys_data->domain_data) { > + /* > + * 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. > + */ > constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns; > - > - if (constraint_ns < 0) { > + } else { > + /* > + * The child is not in a domain and there's no info on its > + * suspend/resume latencies, so assume them to be negligible and > + * take its current PM QoS constraint (that's the only thing > + * known at this point anyway). > + */ > constraint_ns = dev_pm_qos_read_value(dev); > - constraint_ns *= NSEC_PER_USEC; > + if (constraint_ns > 0) > + constraint_ns *= NSEC_PER_USEC; > } > + > + /* 0 means "no constraint" */ > if (constraint_ns == 0) > return 0; > > - /* > - * constraint_ns cannot be negative here, because the device has been > - * suspended. > - */ > if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0) > *constraint_ns_p = constraint_ns; > > @@ -76,14 +87,32 @@ 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 if (constraint_ns < 0) { > + /* > + * This triggers if one of the children that don't belong to a > + * domain has a negative PM QoS constraint and it's better not > + * to suspend then. effective_constraint_ns is negative already > + * and cached_suspend_ok is false, so bail out. > + */ > + return false; This change is ok. However, would like to bring to your attention a possible inconsistency in the treatment of negative value as "no suspend at all" that can affect this. user level entry does not allow negative values. Only way to enter a negative value is if the kernel API to add/update is used. In that interface, if -1 (PM_QOS_DEFAULT_VALUE) is passed, pm_qos_update_target will actually assign the default value stored in the constraint. The default value is PM_QOS_RESUME_LATENCY_DEFAULT_VALUE which is 0. 0 means "no constraint". All this gets fixed in the next patch though. > + } else { > 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 +173,16 @@ 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; > > Regards, Ramesh