Re: [PATCH v3 3/4] arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTINGand pv_time_ops

From: Marc Zyngier
Date: Wed May 08 2013 - 12:03:57 EST


Hi Stefano,

On 08/05/13 16:41, Stefano Stabellini wrote:
> Introduce CONFIG_PARAVIRT and PARAVIRT_TIME_ACCOUNTING on ARM.
>
> The only paravirt interface supported is pv_time_ops.steal_clock, so no
> runtime pvops patching needed.
>
> This allows us to make use of steal_account_process_tick for stolen
> ticks accounting.
>
> Changes in v3:
> - improve commit description and Kconfig help text;
> - no need to initialize pv_time_ops;
> - add PARAVIRT_TIME_ACCOUNTING.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> CC: linux@xxxxxxxxxxxxxxxx
> CC: will.deacon@xxxxxxx
> CC: nico@xxxxxxxxxx
> CC: marc.zyngier@xxxxxxx
> CC: cov@xxxxxxxxxxxxxx
> CC: arnd@xxxxxxxx
> CC: olof@xxxxxxxxx
> ---
> arch/arm/Kconfig | 20 ++++++++++++++++++++
> arch/arm/include/asm/paravirt.h | 19 +++++++++++++++++++
> arch/arm/kernel/Makefile | 1 +
> arch/arm/kernel/paravirt.c | 25 +++++++++++++++++++++++++
> 4 files changed, 65 insertions(+), 0 deletions(-)
> create mode 100644 arch/arm/include/asm/paravirt.h
> create mode 100644 arch/arm/kernel/paravirt.c
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 344e299..89ee2f1 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1887,12 +1887,32 @@ config XEN_DOM0
> def_bool y
> depends on XEN
>
> +config PARAVIRT
> + bool "Enable paravirtualization code"
> + ---help---
> + This changes the kernel so it can modify itself when it is run
> + under a hypervisor, potentially improving performance significantly
> + over full virtualization.
> +
> +config PARAVIRT_TIME_ACCOUNTING
> + bool "Paravirtual steal time accounting"
> + select PARAVIRT

Surely you meant "depends on" instead of "select" here? Otherwise I
don't really see the point of PARAVIRT...

> + default n
> + ---help---
> + Select this option to enable fine granularity task steal time
> + accounting. Time spent executing other tasks in parallel with
> + the current vCPU is discounted from the vCPU power. To account for
> + that, there can be a small performance impact.
> +
> + If in doubt, say N here.
> +
> config XEN
> bool "Xen guest support on ARM (EXPERIMENTAL)"
> depends on ARM && AEABI && OF
> depends on CPU_V7 && !CPU_V6
> depends on !GENERIC_ATOMIC64
> select ARM_PSCI
> + select PARAVIRT
> help
> Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.
>
--
Jazz is not dead. It just smells funny...

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