From: Claude.Yen <Claude.Yen@mediatek.com> To: "Rafael J. Wysocki" <rafael@kernel.org> Cc: wsd_upstream <wsd_upstream@mediatek.com>, Linux PM <linux-pm@vger.kernel.org>, Frederic Weisbecker <fweisbec@gmail.com>, Daniel Lezcano <daniel.lezcano@linaro.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Douglas Anderson <dianders@chromium.org>, Bjorn Andersson <bjorn.andersson@linaro.org>, "moderated list:ARM/Mediatek SoC..." <linux-mediatek@lists.infradead.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Matthias Brugger <matthias.bgg@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Stephen Boyd <swboyd@chromium.org>, Ingo Molnar <mingo@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org> Subject: Re: [PATCH] PM: s2idle: Introduce syscore callbacks in s2idle flow Date: Thu, 3 Sep 2020 10:14:07 +0800 [thread overview] Message-ID: <1599099247.4435.4.camel@mtksdccf07> (raw) In-Reply-To: <CAJZ5v0hOGEUamXw124q4CnL67o97qRHy9Vv9_F2AQqefDdu3vQ@mail.gmail.com> On Tue, 2020-09-01 at 13:57 +0200, Rafael J. Wysocki wrote: > On Tue, Sep 1, 2020 at 9:05 AM Claude Yen <claude.yen@mediatek.com> wrote: > > > > This series based on 5.9-rc1 > > This patch makes s2idle call existing syscore callbacks. Currently, > > when s2idle is selected as system suspend method, callbacks hooked > > by register_syscore_ops() will not be triggered. This may induce > > unexpected results. > > They are not executed by design. > > > For example, sched_clock_suspend() was added to s2idle flow in > > commit 3f2552f7e9c5 ("timers/sched_clock: Prevent generic sched_clock > > wrap caused by tick_freeze()") to fix clock wrap problem. However, > > sched_clock_suspend() is originally registered in syscore callback. > > I'm not sure why this matters here. If functions in syscore callbacks are needed in s2idle, explicit migration is needed like commit 3f2552f7e9c5 ("timers/sched_clock: Prevent generic sched_clock wrap caused by tick_freeze()"). Thus, I am wondering if such effort could be saved. > > With this patch, if another syscore callback is needed in s2idle, > > additional migration effort could be saved. > > s2idle cannot execute syscore callbacks, because it doesn' take > non-boot CPUs offline and it won't do that. > > Thanks! Yes, the current design of syscore callback needs non-boot CPUs offline. Considering the following case: in s2idle flow, there is a status that only one CPU is alive and other CPUs have enter deepest idle state. This situation is similar to getting non-boot CPUs offline, though all CPUs are online from kernel's perspective. Reply from Stephen mentioned that if an operation is needed in both S2R and s2idle, CPU_PM notifier can be utilized. In my opinion, CPU_PM notifier is particularly for CPU entering idle state. In contrast, syscore callback is for system going low power state. There exists semantic difference between these two callbacks. Could the current design of syscore callback be re-designed as system-wide suspend callback? Proposed suspend flow in this patch: Freeze tasks | V Device suspend callbacks | |-------------s2idle---------- | | V | Disable nonboot CPUs Is this CPU last core to enter idle? | | V |------------- syscore callbacks | | | No Yes V | | platform suspend V V enter idle syscore callback | V enter idle Regards, Claude _______________________________________________ Linux-mediatek mailing list Linux-mediatek@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-mediatek
WARNING: multiple messages have this Message-ID (diff)
From: Claude.Yen <Claude.Yen@mediatek.com> To: "Rafael J. Wysocki" <rafael@kernel.org> Cc: wsd_upstream <wsd_upstream@mediatek.com>, Linux PM <linux-pm@vger.kernel.org>, Frederic Weisbecker <fweisbec@gmail.com>, Daniel Lezcano <daniel.lezcano@linaro.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Douglas Anderson <dianders@chromium.org>, Bjorn Andersson <bjorn.andersson@linaro.org>, "moderated list:ARM/Mediatek SoC..." <linux-mediatek@lists.infradead.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Matthias Brugger <matthias.bgg@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Stephen Boyd <swboyd@chromium.org>, Ingo Molnar <mingo@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org> Subject: Re: [PATCH] PM: s2idle: Introduce syscore callbacks in s2idle flow Date: Thu, 3 Sep 2020 10:14:07 +0800 [thread overview] Message-ID: <1599099247.4435.4.camel@mtksdccf07> (raw) In-Reply-To: <CAJZ5v0hOGEUamXw124q4CnL67o97qRHy9Vv9_F2AQqefDdu3vQ@mail.gmail.com> On Tue, 2020-09-01 at 13:57 +0200, Rafael J. Wysocki wrote: > On Tue, Sep 1, 2020 at 9:05 AM Claude Yen <claude.yen@mediatek.com> wrote: > > > > This series based on 5.9-rc1 > > This patch makes s2idle call existing syscore callbacks. Currently, > > when s2idle is selected as system suspend method, callbacks hooked > > by register_syscore_ops() will not be triggered. This may induce > > unexpected results. > > They are not executed by design. > > > For example, sched_clock_suspend() was added to s2idle flow in > > commit 3f2552f7e9c5 ("timers/sched_clock: Prevent generic sched_clock > > wrap caused by tick_freeze()") to fix clock wrap problem. However, > > sched_clock_suspend() is originally registered in syscore callback. > > I'm not sure why this matters here. If functions in syscore callbacks are needed in s2idle, explicit migration is needed like commit 3f2552f7e9c5 ("timers/sched_clock: Prevent generic sched_clock wrap caused by tick_freeze()"). Thus, I am wondering if such effort could be saved. > > With this patch, if another syscore callback is needed in s2idle, > > additional migration effort could be saved. > > s2idle cannot execute syscore callbacks, because it doesn' take > non-boot CPUs offline and it won't do that. > > Thanks! Yes, the current design of syscore callback needs non-boot CPUs offline. Considering the following case: in s2idle flow, there is a status that only one CPU is alive and other CPUs have enter deepest idle state. This situation is similar to getting non-boot CPUs offline, though all CPUs are online from kernel's perspective. Reply from Stephen mentioned that if an operation is needed in both S2R and s2idle, CPU_PM notifier can be utilized. In my opinion, CPU_PM notifier is particularly for CPU entering idle state. In contrast, syscore callback is for system going low power state. There exists semantic difference between these two callbacks. Could the current design of syscore callback be re-designed as system-wide suspend callback? Proposed suspend flow in this patch: Freeze tasks | V Device suspend callbacks | |-------------s2idle---------- | | V | Disable nonboot CPUs Is this CPU last core to enter idle? | | V |------------- syscore callbacks | | | No Yes V | | platform suspend V V enter idle syscore callback | V enter idle Regards, Claude _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-09-03 2:14 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-09-01 7:04 [PATCH] PM: s2idle: Introduce syscore callbacks in s2idle flow Claude Yen 2020-09-01 7:04 ` Claude Yen 2020-09-01 7:04 ` Claude Yen 2020-09-01 7:04 ` [PATCH 1/1] " Claude Yen 2020-09-01 7:04 ` Claude Yen 2020-09-01 7:40 ` Stephen Boyd 2020-09-01 7:40 ` Stephen Boyd 2020-09-03 3:43 ` Claude.Yen 2020-09-03 3:43 ` Claude.Yen 2020-09-01 11:57 ` [PATCH] " Rafael J. Wysocki 2020-09-01 11:57 ` Rafael J. Wysocki 2020-09-01 11:57 ` Rafael J. Wysocki 2020-09-03 2:14 ` Claude.Yen [this message] 2020-09-03 2:14 ` Claude.Yen 2020-09-10 12:55 ` Rafael J. Wysocki 2020-09-10 12:55 ` Rafael J. Wysocki 2020-09-10 12:55 ` Rafael J. Wysocki
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