| Message ID | 20170717142718.13853-12-cdall@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 17/07/17 15:27, Christoffer Dall wrote: > It is currently unclear how to set the VCPU affinity for an interrupt > which is of the per-CPU kind, since the Linux irq_data structure very minor nit (which I should have noticed before, my bad): we have two kinds of per-CPU interrupts in the kernel. percpu, and percpu_devid. For the percpu variety, the IRQ number represents a single interrupt line, delivered to a given CPU (and non migrate-able). The percpu_devid variant represents multiple interrupts, each assigned to one CPU. It'd be nice if the commit message (and the comment below) reflected this distinction. > describes the state for multiple interrupts when the interrupt is a > per-CPU interrupt, 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 > per-CPU 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 per-CPU 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 per-CPU (PPI) interrupt. > > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Marc Zyngier <marc.zyngier@arm.com> > Signed-off-by: Christoffer Dall <cdall@linaro.org> > --- > kernel/irq/manage.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c > index 5624b2d..050b9f6 100644 > --- a/kernel/irq/manage.c > +++ b/kernel/irq/manage.c > @@ -381,7 +381,8 @@ int irq_select_affinity_usr(unsigned int irq) > /** > * irq_set_vcpu_affinity - Set vcpu affinity for the interrupt > * @irq: interrupt number to set affinity > - * @vcpu_info: vCPU specific data > + * @vcpu_info: vCPU specific data or pointer to a percpu array of vCPU > + * specific data for per-CPU interrupts > * > * This function uses the vCPU specific data to set the vCPU > * affinity for an irq. The vCPU specific data is passed from > Otherwise a worthy clarification of the feature. Thanks, M.
On Tue, Aug 01, 2017 at 05:15:39PM +0100, Marc Zyngier wrote: > On 17/07/17 15:27, Christoffer Dall wrote: > > It is currently unclear how to set the VCPU affinity for an interrupt > > which is of the per-CPU kind, since the Linux irq_data structure > > very minor nit (which I should have noticed before, my bad): we have two > kinds of per-CPU interrupts in the kernel. percpu, and percpu_devid. For > the percpu variety, the IRQ number represents a single interrupt line, > delivered to a given CPU (and non migrate-able). The percpu_devid > variant represents multiple interrupts, each assigned to one CPU. > > It'd be nice if the commit message (and the comment below) reflected > this distinction. > > > describes the state for multiple interrupts when the interrupt is a > > per-CPU interrupt, 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 > > per-CPU 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 per-CPU 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 per-CPU (PPI) interrupt. > > > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: Marc Zyngier <marc.zyngier@arm.com> > > Signed-off-by: Christoffer Dall <cdall@linaro.org> > > --- > > kernel/irq/manage.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c > > index 5624b2d..050b9f6 100644 > > --- a/kernel/irq/manage.c > > +++ b/kernel/irq/manage.c > > @@ -381,7 +381,8 @@ int irq_select_affinity_usr(unsigned int irq) > > /** > > * irq_set_vcpu_affinity - Set vcpu affinity for the interrupt > > * @irq: interrupt number to set affinity > > - * @vcpu_info: vCPU specific data > > + * @vcpu_info: vCPU specific data or pointer to a percpu array of vCPU > > + * specific data for per-CPU interrupts > > * > > * This function uses the vCPU specific data to set the vCPU > > * affinity for an irq. The vCPU specific data is passed from > > > > Otherwise a worthy clarification of the feature. > Thanks, I'll try to clarify based on the info below. Linux IRQ abstractions; I know nothing. -Christoffer
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index 5624b2d..050b9f6 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -381,7 +381,8 @@ int irq_select_affinity_usr(unsigned int irq) /** * irq_set_vcpu_affinity - Set vcpu affinity for the interrupt * @irq: interrupt number to set affinity - * @vcpu_info: vCPU specific data + * @vcpu_info: vCPU specific data or pointer to a percpu array of vCPU + * specific data for per-CPU interrupts * * This function uses the vCPU specific data to set the vCPU * affinity for an irq. The vCPU specific data is passed from
It is currently unclear how to set the VCPU affinity for an interrupt which is of the per-CPU kind, since the Linux irq_data structure describes the state for multiple interrupts when the interrupt is a per-CPU interrupt, 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 per-CPU 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 per-CPU 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 per-CPU (PPI) interrupt. Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Christoffer Dall <cdall@linaro.org> --- kernel/irq/manage.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)