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From: Valentin Schneider <valentin.schneider@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Android Kernel Team <kernel-team@android.com>,
	Russell King <linux@arm.linux.org.uk>,
	Marc Zyngier <maz@kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	LAK <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 2/6] genirq: Allow an interrupt to be marked as 'raw'
Date: Sat, 05 Dec 2020 19:24:15 +0000	[thread overview]
Message-ID: <jhjv9dgt5sw.mognet@arm.com> (raw)
In-Reply-To: <jhjy2ieubsj.mognet@arm.com>


On 03/12/20 15:52, Valentin Schneider wrote:
> On 03/12/20 13:03, Peter Zijlstra wrote:
[...]
>> The scheduler IPI really doesn't need RCU either ;-)
[...]
> But as with any other interrupt, we could then go through:
>
>   preempt_schedule_irq() ~> pick_next_task_fair() -> newidle_balance()
>
> which does enter a read-side section, so RCU would need to be
> watching. Looking at kernel/entry/common.c:irqentry_exit_cond_resched(), it
> seems we do check for this via rcu_irq_exit_check_preempt().
>
> I however cannot grok why irqentry_exit() *doesn't* call into
> preempt_schedule_irq() if RCU wasn't watching on IRQ entry

RCU wasn't watching on IRQ entry:
  -> we should be on the idle task
  -> no unvoluntary preemption for the idle task, scheduling always happens
     at the tail of the idle loop
  -> ignore what I've been saying, current patch is fine

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WARNING: multiple messages have this Message-ID (diff)
From: Valentin Schneider <valentin.schneider@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Marc Zyngier <maz@kernel.org>,
	LAK <linux-arm-kernel@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Mark Rutland <mark.rutland@arm.com>,
	Russell King <linux@arm.linux.org.uk>,
	Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH v2 2/6] genirq: Allow an interrupt to be marked as 'raw'
Date: Sat, 05 Dec 2020 19:24:15 +0000	[thread overview]
Message-ID: <jhjv9dgt5sw.mognet@arm.com> (raw)
In-Reply-To: <jhjy2ieubsj.mognet@arm.com>


On 03/12/20 15:52, Valentin Schneider wrote:
> On 03/12/20 13:03, Peter Zijlstra wrote:
[...]
>> The scheduler IPI really doesn't need RCU either ;-)
[...]
> But as with any other interrupt, we could then go through:
>
>   preempt_schedule_irq() ~> pick_next_task_fair() -> newidle_balance()
>
> which does enter a read-side section, so RCU would need to be
> watching. Looking at kernel/entry/common.c:irqentry_exit_cond_resched(), it
> seems we do check for this via rcu_irq_exit_check_preempt().
>
> I however cannot grok why irqentry_exit() *doesn't* call into
> preempt_schedule_irq() if RCU wasn't watching on IRQ entry

RCU wasn't watching on IRQ entry:
  -> we should be on the idle task
  -> no unvoluntary preemption for the idle task, scheduling always happens
     at the tail of the idle loop
  -> ignore what I've been saying, current patch is fine

  reply	other threads:[~2020-12-05 19:25 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-24 14:14 [PATCH v2 0/6] arm/arm64: Allow the rescheduling IPI to bypass irq_enter/exit Marc Zyngier
2020-11-24 14:14 ` Marc Zyngier
2020-11-24 14:14 ` [PATCH v2 1/6] genirq: Add __irq_modify_status() helper to clear/set special flags Marc Zyngier
2020-11-24 14:14   ` Marc Zyngier
2020-11-24 14:14 ` [PATCH v2 2/6] genirq: Allow an interrupt to be marked as 'raw' Marc Zyngier
2020-11-24 14:14   ` Marc Zyngier
2020-11-24 16:26   ` Peter Zijlstra
2020-11-24 16:26     ` Peter Zijlstra
2020-11-24 16:56     ` Marc Zyngier
2020-11-24 16:56       ` Marc Zyngier
2020-11-26 18:18   ` Valentin Schneider
2020-11-26 18:18     ` Valentin Schneider
2020-12-03 13:03     ` Peter Zijlstra
2020-12-03 13:03       ` Peter Zijlstra
2020-12-03 15:52       ` Valentin Schneider
2020-12-03 15:52         ` Valentin Schneider
2020-12-05 19:24         ` Valentin Schneider [this message]
2020-12-05 19:24           ` Valentin Schneider
2020-12-10 15:07   ` Will Deacon
2020-12-10 15:07     ` Will Deacon
2021-06-23 17:28   ` Todd Kjos
2021-06-23 17:28     ` Todd Kjos
2020-11-24 14:14 ` [PATCH v2 3/6] arm64: Mark the recheduling IPI as raw interrupt Marc Zyngier
2020-11-24 14:14   ` Marc Zyngier
2020-12-10 15:15   ` Will Deacon
2020-12-10 15:15     ` Will Deacon
2020-11-24 14:14 ` [PATCH v2 4/6] arm: " Marc Zyngier
2020-11-24 14:14   ` Marc Zyngier
2020-11-24 14:14 ` [PATCH v2 5/6] genirq: Drop IRQ_HIDDEN from IRQF_MODIFY_MASK Marc Zyngier
2020-11-24 14:14   ` Marc Zyngier
2020-11-24 14:14 ` [PATCH v2 6/6] genirq: Rename IRQ_HIDDEN to IRQ_IPI Marc Zyngier
2020-11-24 14:14   ` Marc Zyngier
2020-11-26 18:18   ` Valentin Schneider
2020-11-26 18:18     ` Valentin Schneider
2021-03-01  0:39 ` [PATCH v2 0/6] arm/arm64: Allow the rescheduling IPI to bypass irq_enter/exit ito-yuichi
2021-03-01  0:39   ` ito-yuichi
2021-03-01  9:22   ` Marc Zyngier
2021-03-01  9:22     ` Marc Zyngier
2021-03-09  6:20     ` Yuichi Ito
2021-03-09  6:20       ` Yuichi Ito
2021-06-18 19:30 ` Abhijeet Dharmapurikar

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