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From: Valentin Schneider <valentin.schneider@arm.com>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Sumit Garg <sumit.garg@linaro.org>,
	kernel-team@android.com, Jason Cooper <jason@lakedaemon.net>,
	Marc Zyngier <maz@kernel.org>,
	linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 04/11] ARM: Allow IPIs to be handled as normal interrupts
Date: Thu, 21 May 2020 15:03:49 +0100
Message-ID: <jhjk115xu4a.mognet@arm.com> (raw)
In-Reply-To: <20200519222447.GJ1551@shell.armlinux.org.uk>


On 19/05/20 23:24, Russell King - ARM Linux admin wrote:
> On Tue, May 19, 2020 at 05:17:48PM +0100, Marc Zyngier wrote:
>> In order to deal with IPIs as normal interrupts, let's add
>> a new way to register them with the architecture code.
>>
>> set_smp_ipi_range() takes a range of interrupts, and allows
>> the arch code to request them as if the were normal interrupts.
>> A standard handler is then called by the core IRQ code to deal
>> with the IPI.
>>
>> This means that we don't need to call irq_enter/irq_exit, and
>> that we don't need to deal with set_irq_regs either. So let's
>> move the dispatcher into its own function, and leave handle_IPI()
>> as a compatibility function.
>>
>> On the sending side, let's make use of ipi_send_mask, which
>> already exists for this purpose.
>
> You say nothing about the nesting of irq_enter() and irq_exit()
> for scheduler_ipi().
>
> Given that lockdep introduced the requirement that hard IRQs can't
> be nested, are we sure that calling irq_exit() twice is safe?
>
> Looking at irqtime_account_irq(), it seems that will cause double-
> accounting of in-interrupt time, since we will increment
> irq_start_time by just over twice the the period spent handling
> the IPI.
>
> I think the rest of irq_exit() should be safe, but still, this
> behaviour should be documented at the very least, if not avoided.
>

x86 does the same (though IIUC only when tracing reschedule IPI's), and
MIPS has the same issue as it also uses generic IRQ IPI's - so although
it's not ideal, I think we can live with it.

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Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-19 16:17 [PATCH 00/11] arm/arm64: Turning IPIs into " Marc Zyngier
2020-05-19 16:17 ` [PATCH 01/11] genirq: Add fasteoi IPI flow Marc Zyngier
2020-05-19 19:47   ` Florian Fainelli
2020-06-12  9:54     ` Marc Zyngier
2020-05-19 22:25   ` Valentin Schneider
2020-05-19 22:29     ` Valentin Schneider
2020-06-12  9:58     ` Marc Zyngier
2020-05-19 16:17 ` [PATCH 02/11] genirq: Allow interrupts to be excluded from /proc/interrupts Marc Zyngier
2020-05-19 16:17 ` [PATCH 03/11] arm64: Allow IPIs to be handled as normal interrupts Marc Zyngier
2020-05-21 14:03   ` Valentin Schneider
2020-05-19 16:17 ` [PATCH 04/11] ARM: " Marc Zyngier
2020-05-19 22:24   ` Russell King - ARM Linux admin
2020-05-21 14:03     ` Valentin Schneider [this message]
2020-05-21 15:12       ` Russell King - ARM Linux admin
2020-05-21 16:11         ` Valentin Schneider
2020-05-19 16:17 ` [PATCH 05/11] irqchip/gic-v3: Describe the SGI range Marc Zyngier
2020-05-19 16:17 ` [PATCH 06/11] irqchip/gic-v3: Configure SGIs as standard interrupts Marc Zyngier
2020-05-20  9:52   ` Sumit Garg
2020-05-20 10:24     ` Marc Zyngier
2020-05-21 14:04   ` Valentin Schneider
2020-06-12 10:39     ` Marc Zyngier
2020-05-19 16:17 ` [PATCH 07/11] irqchip/gic: Refactor SMP configuration Marc Zyngier
2020-05-19 16:17 ` [PATCH 08/11] irqchip/gic: Configure SGIs as standard interrupts Marc Zyngier
2021-04-20 20:37   ` dann frazier
2021-04-20 21:25     ` dann frazier
2021-04-21 10:58       ` Marc Zyngier
2021-04-21 14:52         ` dann frazier
2021-04-21 15:49           ` Marc Zyngier
2020-05-19 16:17 ` [PATCH 09/11] irqchip/gic-common: Don't enable SGIs by default Marc Zyngier
2020-05-19 16:17 ` [PATCH 10/11] irqchip/bcm2836: Configure mailbox interrupts as standard interrupts Marc Zyngier
2020-05-19 16:17 ` [PATCH 11/11] arm64: Kill __smp_cross_call and co Marc Zyngier
2020-05-19 17:50 ` [PATCH 00/11] arm/arm64: Turning IPIs into normal interrupts Florian Fainelli
2020-05-19 19:47   ` Florian Fainelli
2020-06-12  9:49   ` Marc Zyngier
2020-06-12 16:57     ` Florian Fainelli
2020-05-19 22:25 ` Valentin Schneider

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