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

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Wed, 8 May 2013, Marc Zyngier wrote:
> 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@eu.citrix.com>
> > CC: linux@arm.linux.org.uk
> > CC: will.deacon@arm.com
> > CC: nico@linaro.org
> > CC: marc.zyngier@arm.com
> > CC: cov@codeaurora.org
> > CC: arnd@arndb.de
> > CC: olof@lixom.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...

I agree with you that "depends on" seems to be the right thing here, but
on x86 is actually select.

The original commit is 095c0aa83e52d6c3dd7168610746703921f570af.