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From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kevin Hilman <khilman@kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Adrien Thierry <athierry@redhat.com>,
	Brian Masney <bmasney@redhat.com>,
	linux-rt-users@vger.kernel.org
Subject: Re: [PATCH v2 3/5] cpuidle: psci: Do not suspend topology CPUs on PREEMPT_RT
Date: Thu, 12 Jan 2023 12:34:35 +0100	[thread overview]
Message-ID: <3d7c3a52-baa4-ce7b-e6d1-06a4d885d445@linaro.org> (raw)
In-Reply-To: <Y7/qZNoXvp/I6h8s@linutronix.de>

On 12/01/2023 12:09, Sebastian Andrzej Siewior wrote:
> On 2022-12-19 16:15:01 [+0100], Krzysztof Kozlowski wrote:
>> diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
>> index 57bc3e3ae391..9d971cc4b12b 100644
>> --- a/drivers/cpuidle/cpuidle-psci.c
>> +++ b/drivers/cpuidle/cpuidle-psci.c
>> @@ -72,7 +72,7 @@ static int __psci_enter_domain_idle_state(struct cpuidle_device *dev,
>>  	ct_irq_enter_irqson();
>>  	if (s2idle)
>>  		dev_pm_genpd_suspend(pd_dev);
>> -	else
>> +	else if (!IS_ENABLED(CONFIG_PREEMPT_RT))
>>  		pm_runtime_put_sync_suspend(pd_dev);
> 
> So based on the commit description you run into a sleeping lock in
> pm_runtime_put_sync_suspend() while the CPU is in an IRQ-off region.
> Why is it okay to skip it on PREEMPT_RT?

It is okay to skip it everywhere, you just don't get a suspended CPU.
Why PREEMPT_RT is different here - having suspended CPU is a great way
to have longer or even unpredictable (as it goes to firmware which is
out of control of Linux) latencies.

Best regards,
Krzysztof


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linux-arm-kernel@lists.infradead.org
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WARNING: multiple messages have this Message-ID (diff)
From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kevin Hilman <khilman@kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Adrien Thierry <athierry@redhat.com>,
	Brian Masney <bmasney@redhat.com>,
	linux-rt-users@vger.kernel.org
Subject: Re: [PATCH v2 3/5] cpuidle: psci: Do not suspend topology CPUs on PREEMPT_RT
Date: Thu, 12 Jan 2023 12:34:35 +0100	[thread overview]
Message-ID: <3d7c3a52-baa4-ce7b-e6d1-06a4d885d445@linaro.org> (raw)
In-Reply-To: <Y7/qZNoXvp/I6h8s@linutronix.de>

On 12/01/2023 12:09, Sebastian Andrzej Siewior wrote:
> On 2022-12-19 16:15:01 [+0100], Krzysztof Kozlowski wrote:
>> diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
>> index 57bc3e3ae391..9d971cc4b12b 100644
>> --- a/drivers/cpuidle/cpuidle-psci.c
>> +++ b/drivers/cpuidle/cpuidle-psci.c
>> @@ -72,7 +72,7 @@ static int __psci_enter_domain_idle_state(struct cpuidle_device *dev,
>>  	ct_irq_enter_irqson();
>>  	if (s2idle)
>>  		dev_pm_genpd_suspend(pd_dev);
>> -	else
>> +	else if (!IS_ENABLED(CONFIG_PREEMPT_RT))
>>  		pm_runtime_put_sync_suspend(pd_dev);
> 
> So based on the commit description you run into a sleeping lock in
> pm_runtime_put_sync_suspend() while the CPU is in an IRQ-off region.
> Why is it okay to skip it on PREEMPT_RT?

It is okay to skip it everywhere, you just don't get a suspended CPU.
Why PREEMPT_RT is different here - having suspended CPU is a great way
to have longer or even unpredictable (as it goes to firmware which is
out of control of Linux) latencies.

Best regards,
Krzysztof


  reply	other threads:[~2023-01-12 11:35 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-19 15:14 [PATCH v2 0/5] PM: Fixes for Realtime systems Krzysztof Kozlowski
2022-12-19 15:14 ` Krzysztof Kozlowski
2022-12-19 15:14 ` [PATCH v2 1/5] PM: domains: Add GENPD_FLAG_RT_SAFE for PREEMPT_RT Krzysztof Kozlowski
2022-12-19 15:14   ` Krzysztof Kozlowski
2023-01-04 15:45   ` Ulf Hansson
2023-01-04 15:45     ` Ulf Hansson
2023-01-06 14:52     ` Krzysztof Kozlowski
2023-01-06 14:52       ` Krzysztof Kozlowski
2023-01-12 10:36       ` Sebastian Andrzej Siewior
2023-01-12 10:36         ` Sebastian Andrzej Siewior
2023-01-12 11:27         ` Krzysztof Kozlowski
2023-01-12 11:27           ` Krzysztof Kozlowski
2023-01-12 10:32   ` Sebastian Andrzej Siewior
2023-01-12 10:32     ` Sebastian Andrzej Siewior
2023-01-12 11:31     ` Krzysztof Kozlowski
2023-01-12 11:31       ` Krzysztof Kozlowski
2022-12-19 15:15 ` [PATCH v2 2/5] cpuidle: psci: Mark as PREEMPT_RT safe Krzysztof Kozlowski
2022-12-19 15:15   ` Krzysztof Kozlowski
2023-01-12 11:00   ` Sebastian Andrzej Siewior
2023-01-12 11:00     ` Sebastian Andrzej Siewior
2023-01-12 11:32     ` Krzysztof Kozlowski
2023-01-12 11:32       ` Krzysztof Kozlowski
2023-01-17 15:27   ` Ulf Hansson
2023-01-17 15:27     ` Ulf Hansson
2023-01-19 15:40     ` Krzysztof Kozlowski
2023-01-19 15:40       ` Krzysztof Kozlowski
2023-01-19 17:06       ` Krzysztof Kozlowski
2023-01-19 17:06         ` Krzysztof Kozlowski
2022-12-19 15:15 ` [PATCH v2 3/5] cpuidle: psci: Do not suspend topology CPUs on PREEMPT_RT Krzysztof Kozlowski
2022-12-19 15:15   ` Krzysztof Kozlowski
2023-01-12 11:09   ` Sebastian Andrzej Siewior
2023-01-12 11:09     ` Sebastian Andrzej Siewior
2023-01-12 11:34     ` Krzysztof Kozlowski [this message]
2023-01-12 11:34       ` Krzysztof Kozlowski
2023-01-30  9:51       ` Sebastian Andrzej Siewior
2023-01-30  9:51         ` Sebastian Andrzej Siewior
2022-12-19 15:15 ` [PATCH v2 4/5] PM: Allow calling dev_pm_domain_set() with raw spinlock Krzysztof Kozlowski
2022-12-19 15:15   ` Krzysztof Kozlowski
2023-01-12 11:13   ` Sebastian Andrzej Siewior
2023-01-12 11:13     ` Sebastian Andrzej Siewior
2022-12-19 15:15 ` [PATCH v2 5/5] PM: domains: Do not call device_pm_check_callbacks() when holding genpd_lock() Krzysztof Kozlowski
2022-12-19 15:15   ` Krzysztof Kozlowski
2023-01-12 11:31   ` Sebastian Andrzej Siewior
2023-01-12 11:31     ` Sebastian Andrzej Siewior
2023-01-12 11:37     ` Krzysztof Kozlowski
2023-01-12 11:37       ` Krzysztof Kozlowski
2023-01-17 15:11   ` Ulf Hansson
2023-01-17 15:11     ` Ulf Hansson
2023-01-19 15:58     ` Krzysztof Kozlowski
2023-01-19 15:58       ` Krzysztof Kozlowski
2022-12-20 21:36 ` [PATCH v2 0/5] PM: Fixes for Realtime systems Adrien Thierry
2022-12-20 21:36   ` Adrien Thierry
2023-01-04 15:15   ` Ulf Hansson
2023-01-04 15:15     ` Ulf Hansson

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