[Qemu-devel] [PATCH] virt-acpi-build: add always-on property for timer

[Qemu-devel] [PATCH] virt-acpi-build: add always-on property for timer

[Andrew Jones]

This patch is the ACPI equivalent of "hw/arm/virt: Add always-on
property to the virt board timer". The timer is always on, and
thus setting this informs Linux that it may switch off the periodic
timer. Switching off the periodic timer substantially reduces the
number of interrupts the host needs to inject.

Testing note: AArch64 guests (the only ones currently booting with
ACPI) do not actually need this patch to determine it can turn the
periodic timer off. I therefore used a hacked guest kernel to ensure
this patch works as the equivalent DT patch does.

Signed-off-by: Andrew Jones <drjones@redhat.com>
---
 hw/arm/virt-acpi-build.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 87fbe7c97d99b..f6e538f3d02ea 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -443,7 +443,7 @@ build_gtdt(GArray *table_data, GArray *linker)
     gtdt->secure_el1_flags = ACPI_EDGE_SENSITIVE;
 
     gtdt->non_secure_el1_interrupt = ARCH_TIMER_NS_EL1_IRQ + 16;
-    gtdt->non_secure_el1_flags = ACPI_EDGE_SENSITIVE;
+    gtdt->non_secure_el1_flags = ACPI_EDGE_SENSITIVE | ACPI_GTDT_ALWAYS_ON;
 
     gtdt->virtual_timer_interrupt = ARCH_TIMER_VIRT_IRQ + 16;
     gtdt->virtual_timer_flags = ACPI_EDGE_SENSITIVE;
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH] virt-acpi-build: add always-on property for timer

[Shannon Zhao]

On 2016/1/21 20:54, Andrew Jones wrote:
> This patch is the ACPI equivalent of "hw/arm/virt: Add always-on
> property to the virt board timer". The timer is always on, and
> thus setting this informs Linux that it may switch off the periodic
> timer. Switching off the periodic timer substantially reduces the
> number of interrupts the host needs to inject.
> 
> Testing note: AArch64 guests (the only ones currently booting with
> ACPI) do not actually need this patch to determine it can turn the
> periodic timer off. I therefore used a hacked guest kernel to ensure
> this patch works as the equivalent DT patch does.
> 
Reviewed-by: Shannon Zhao <shannon.zhao@linaro.org>

> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  hw/arm/virt-acpi-build.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 87fbe7c97d99b..f6e538f3d02ea 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -443,7 +443,7 @@ build_gtdt(GArray *table_data, GArray *linker)
>      gtdt->secure_el1_flags = ACPI_EDGE_SENSITIVE;
>  
>      gtdt->non_secure_el1_interrupt = ARCH_TIMER_NS_EL1_IRQ + 16;
> -    gtdt->non_secure_el1_flags = ACPI_EDGE_SENSITIVE;
> +    gtdt->non_secure_el1_flags = ACPI_EDGE_SENSITIVE | ACPI_GTDT_ALWAYS_ON;
>  
>      gtdt->virtual_timer_interrupt = ARCH_TIMER_VIRT_IRQ + 16;
>      gtdt->virtual_timer_flags = ACPI_EDGE_SENSITIVE;
> 

-- 
Shannon

Re: [Qemu-devel] [PATCH] virt-acpi-build: add always-on property for timer

[Peter Maydell]

On 21 January 2016 at 12:54, Andrew Jones <drjones@redhat.com> wrote:
> This patch is the ACPI equivalent of "hw/arm/virt: Add always-on
> property to the virt board timer". The timer is always on, and
> thus setting this informs Linux that it may switch off the periodic
> timer. Switching off the periodic timer substantially reduces the
> number of interrupts the host needs to inject.
>
> Testing note: AArch64 guests (the only ones currently booting with
> ACPI) do not actually need this patch to determine it can turn the
> periodic timer off. I therefore used a hacked guest kernel to ensure
> this patch works as the equivalent DT patch does.
>
> Signed-off-by: Andrew Jones <drjones@redhat.com>



Applied to target-arm.next, thanks.

-- PMM