linux-kernel - Re: [PATCH v3 3/4] arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING and pv_time

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Message-ID: <518A7763.4050509@arm.com>
Date:	Wed, 08 May 2013 17:03:47 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	Will Deacon <Will.Deacon@....com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"nico@...aro.org" <nico@...aro.org>,
	"cov@...eaurora.org" <cov@...eaurora.org>,
	"arnd@...db.de" <arnd@...db.de>, "olof@...om.net" <olof@...om.net>
Subject: Re: [PATCH v3 3/4] arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING
 and pv_time_ops

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@...citrix.com>
> CC: linux@....linux.org.uk
> CC: will.deacon@....com
> CC: nico@...aro.org
> CC: marc.zyngier@....com
> CC: cov@...eaurora.org
> CC: arnd@...db.de
> CC: olof@...om.net
> ---
>  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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