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From: Christoffer Dall <cdall@linaro.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoffer Dall <christoffer.dall@linaro.org>,
	kvm@vger.kernel.org, Marc Zyngier <marc.zyngier@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu,
	Shih-Wei Li <shihwei@cs.columbia.edu>
Subject: Re: [PATCH v4 12/20] genirq: Document vcpu_info usage for percpu_devid interrupts
Date: Sat, 21 Oct 2017 16:29:23 +0200	[thread overview]
Message-ID: <20171021142923.GA12618@cbox> (raw)
In-Reply-To: <alpine.DEB.2.20.1710201354590.2908@nanos>

On Fri, Oct 20, 2017 at 01:56:16PM +0200, Thomas Gleixner wrote:
> On Fri, 20 Oct 2017, Christoffer Dall wrote:
> 
> Please Cc lkml when changing genirq core code.
> 

ok, will do so in the future.

> > It is currently unclear how to set the VCPU affinity for a percpu_devid
> > interrupt , since the Linux irq_data structure describes the state for
> > multiple interrupts, one for each physical CPU on the system.  Since
> > each such interrupt can be associated with different VCPUs or none at
> > all, associating a single VCPU state with such an interrupt does not
> > capture the necessary semantics.
> > 
> > The implementers of irq_set_affinity are the Intel and AMD IOMMUs, and
> > the ARM GIC irqchip.  The Intel and AMD callers do not appear to use
> > percpu_devid interrupts, and the ARM GIC implementation only checks the
> > pointer against NULL vs. non-NULL.
> > 
> > Therefore, simply update the function documentation to explain the
> > expected use in the context of percpu_devid interrupts, allowing future
> > changes or additions to irqchip implementers to do the right thing.
> > 
> > This allows us to set the VCPU affinity for the virtual timer interrupt
> > in KVM/ARM, which is a percpu_devid (PPI) interrupt.
> 
> I have a hard time to understand how adding the comment allows you to set
> VCPU affinity ....
> 

Obviously everything already works without adding the comment, however
it is not entirely clear how to use the vcpu_into for percpu_devid
interrupts, and this patch aims to make that clear, as it is the first
user of irq_set_vcpu_affinity for a percpu_devid interrupt which
actually uses the vcpu_info pointer.

Would you rather that we did not update the documentation or what do you
suggest?

Thanks,
-Christoffer

WARNING: multiple messages have this Message-ID (diff)
From: cdall@linaro.org (Christoffer Dall)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v4 12/20] genirq: Document vcpu_info usage for percpu_devid interrupts
Date: Sat, 21 Oct 2017 16:29:23 +0200	[thread overview]
Message-ID: <20171021142923.GA12618@cbox> (raw)
In-Reply-To: <alpine.DEB.2.20.1710201354590.2908@nanos>

On Fri, Oct 20, 2017 at 01:56:16PM +0200, Thomas Gleixner wrote:
> On Fri, 20 Oct 2017, Christoffer Dall wrote:
> 
> Please Cc lkml when changing genirq core code.
> 

ok, will do so in the future.

> > It is currently unclear how to set the VCPU affinity for a percpu_devid
> > interrupt , since the Linux irq_data structure describes the state for
> > multiple interrupts, one for each physical CPU on the system.  Since
> > each such interrupt can be associated with different VCPUs or none at
> > all, associating a single VCPU state with such an interrupt does not
> > capture the necessary semantics.
> > 
> > The implementers of irq_set_affinity are the Intel and AMD IOMMUs, and
> > the ARM GIC irqchip.  The Intel and AMD callers do not appear to use
> > percpu_devid interrupts, and the ARM GIC implementation only checks the
> > pointer against NULL vs. non-NULL.
> > 
> > Therefore, simply update the function documentation to explain the
> > expected use in the context of percpu_devid interrupts, allowing future
> > changes or additions to irqchip implementers to do the right thing.
> > 
> > This allows us to set the VCPU affinity for the virtual timer interrupt
> > in KVM/ARM, which is a percpu_devid (PPI) interrupt.
> 
> I have a hard time to understand how adding the comment allows you to set
> VCPU affinity ....
> 

Obviously everything already works without adding the comment, however
it is not entirely clear how to use the vcpu_into for percpu_devid
interrupts, and this patch aims to make that clear, as it is the first
user of irq_set_vcpu_affinity for a percpu_devid interrupt which
actually uses the vcpu_info pointer.

Would you rather that we did not update the documentation or what do you
suggest?

Thanks,
-Christoffer

  reply	other threads:[~2017-10-21 14:29 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-20 11:49 [PATCH v4 00/20] KVM: arm/arm64: Optimize arch timer register handling Christoffer Dall
2017-10-20 11:49 ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 01/20] irqchip/gic: Deal with broken firmware exposing only 4kB of GICv2 CPU interface Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 02/20] arm64: Implement arch_counter_get_cntpct to read the physical counter Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-25 13:41   ` Marc Zyngier
2017-10-25 13:41     ` Marc Zyngier
2017-10-20 11:49 ` [PATCH v4 03/20] arm64: Use physical counter for in-kernel reads when booted in EL2 Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-25 13:43   ` Marc Zyngier
2017-10-25 13:43     ` Marc Zyngier
2017-10-20 11:49 ` [PATCH v4 04/20] KVM: arm/arm64: Guard kvm_vgic_map_is_active against !vgic_initialized Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 05/20] KVM: arm/arm64: Support calling vgic_update_irq_pending from irq context Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-25 13:45   ` Marc Zyngier
2017-10-25 13:45     ` Marc Zyngier
2017-10-20 11:49 ` [PATCH v4 06/20] KVM: arm/arm64: Check that system supports split eoi/deactivate Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-25 13:47   ` Marc Zyngier
2017-10-25 13:47     ` Marc Zyngier
2017-10-20 11:49 ` [PATCH v4 07/20] KVM: arm/arm64: Make timer_arm and timer_disarm helpers more generic Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-25 13:49   ` Marc Zyngier
2017-10-25 13:49     ` Marc Zyngier
2017-10-20 11:49 ` [PATCH v4 08/20] KVM: arm/arm64: Rename soft timer to bg_timer Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 09/20] KVM: arm/arm64: Move timer/vgic flush/sync under disabled irq Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 10/20] KVM: arm/arm64: Use separate timer for phys timer emulation Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-25 13:59   ` Marc Zyngier
2017-10-25 13:59     ` Marc Zyngier
2017-10-20 11:49 ` [PATCH v4 11/20] KVM: arm/arm64: Move timer save/restore out of the hyp code Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 12/20] genirq: Document vcpu_info usage for percpu_devid interrupts Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:56   ` Thomas Gleixner
2017-10-20 11:56     ` Thomas Gleixner
2017-10-21 14:29     ` Christoffer Dall [this message]
2017-10-21 14:29       ` Christoffer Dall
2017-10-21 14:55       ` Thomas Gleixner
2017-10-21 14:55         ` Thomas Gleixner
2017-10-21 15:30         ` Christoffer Dall
2017-10-21 15:30           ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 13/20] KVM: arm/arm64: Set VCPU affinity for virt timer irq Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 14/20] KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-25 14:36   ` Marc Zyngier
2017-10-25 14:36     ` Marc Zyngier
2017-11-16 20:30   ` Jintack Lim
2017-11-16 20:30     ` Jintack Lim
2017-11-16 20:32     ` Jintack Lim
2017-11-16 20:32       ` Jintack Lim
2017-11-20 11:15     ` Christoffer Dall
2017-11-20 11:15       ` Christoffer Dall
2017-11-20 16:32       ` Jintack Lim
2017-11-20 16:32         ` Jintack Lim
2017-10-20 11:49 ` [PATCH v4 15/20] KVM: arm/arm64: Support EL1 phys timer register access in set/get reg Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-25 14:38   ` Marc Zyngier
2017-10-25 14:38     ` Marc Zyngier
2017-10-20 11:49 ` [PATCH v4 16/20] KVM: arm/arm64: Use kvm_arm_timer_set/get_reg for guest register traps Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 17/20] KVM: arm/arm64: Move phys_timer_emulate function Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 18/20] KVM: arm/arm64: Avoid phys timer emulation in vcpu entry/exit Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 19/20] KVM: arm/arm64: Get rid of kvm_timer_flush_hwstate Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall
2017-10-20 11:49 ` [PATCH v4 20/20] KVM: arm/arm64: Rework kvm_timer_should_fire Christoffer Dall
2017-10-20 11:49   ` Christoffer Dall

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