Re: [PATCH v11 3/5] arm: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING and pv_time_ops

[Stefano Stabellini]

On Tue, 10 Nov 2015, Stefano Stabellini wrote:
> On Thu, 5 Nov 2015, 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.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > Acked-by: Christopher Covington <cov@xxxxxxxxxxxxxx>
> > Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > CC: linux@xxxxxxxxxxxxxxxx
> > CC: will.deacon@xxxxxxx
> > CC: nico@xxxxxxxxxx
> > CC: marc.zyngier@xxxxxxx
> > CC: cov@xxxxxxxxxxxxxx
> > CC: arnd@xxxxxxxx
> > CC: olof@xxxxxxxxx
> 
> 
> Russell,
> are you OK with this patch?

Russell,

I am going to drop this patch and add a small #ifdef to
arch/arm/xen/enlighten.c to be able to use this functionality on arm64.

If you change your mind let me know.



> 
> 
> > 
> > Changes in v10:
> > - replace "---help---" with "help"
> > 
> > Changes in v7:
> > - ifdef CONFIG_PARAVIRT the content of paravirt.h.
> > 
> > Changes in v3:
> > - improve commit description and Kconfig help text;
> > - no need to initialize pv_time_ops;
> > - add PARAVIRT_TIME_ACCOUNTING.
> > ---
> >  arch/arm/Kconfig                |   20 ++++++++++++++++++++
> >  arch/arm/include/asm/paravirt.h |   20 ++++++++++++++++++++
> >  arch/arm/kernel/Makefile        |    1 +
> >  arch/arm/kernel/paravirt.c      |   25 +++++++++++++++++++++++++
> >  4 files changed, 66 insertions(+)
> >  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 f1ed110..60be104 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -1823,6 +1823,25 @@ config SWIOTLB
> >  config IOMMU_HELPER
> >  	def_bool SWIOTLB
> >  
> > +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
> > +	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_DOM0
> >  	def_bool y
> >  	depends on XEN
> > @@ -1836,6 +1855,7 @@ config XEN
> >  	select ARCH_DMA_ADDR_T_64BIT
> >  	select ARM_PSCI
> >  	select SWIOTLB_XEN
> > +	select PARAVIRT
> >  	help
> >  	  Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.
> >  
> > diff --git a/arch/arm/include/asm/paravirt.h b/arch/arm/include/asm/paravirt.h
> > new file mode 100644
> > index 0000000..8435ff59
> > --- /dev/null
> > +++ b/arch/arm/include/asm/paravirt.h
> > @@ -0,0 +1,20 @@
> > +#ifndef _ASM_ARM_PARAVIRT_H
> > +#define _ASM_ARM_PARAVIRT_H
> > +
> > +#ifdef CONFIG_PARAVIRT
> > +struct static_key;
> > +extern struct static_key paravirt_steal_enabled;
> > +extern struct static_key paravirt_steal_rq_enabled;
> > +
> > +struct pv_time_ops {
> > +	unsigned long long (*steal_clock)(int cpu);
> > +};
> > +extern struct pv_time_ops pv_time_ops;
> > +
> > +static inline u64 paravirt_steal_clock(int cpu)
> > +{
> > +	return pv_time_ops.steal_clock(cpu);
> > +}
> > +#endif
> > +
> > +#endif
> > diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> > index af9e59b..3e6e937 100644
> > --- a/arch/arm/kernel/Makefile
> > +++ b/arch/arm/kernel/Makefile
> > @@ -81,6 +81,7 @@ obj-$(CONFIG_VDSO)		+= vdso.o
> >  ifneq ($(CONFIG_ARCH_EBSA110),y)
> >    obj-y		+= io.o
> >  endif
> > +obj-$(CONFIG_PARAVIRT)	+= paravirt.o
> >  
> >  head-y			:= head$(MMUEXT).o
> >  obj-$(CONFIG_DEBUG_LL)	+= debug.o
> > diff --git a/arch/arm/kernel/paravirt.c b/arch/arm/kernel/paravirt.c
> > new file mode 100644
> > index 0000000..53f371e
> > --- /dev/null
> > +++ b/arch/arm/kernel/paravirt.c
> > @@ -0,0 +1,25 @@
> > +/*
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * Copyright (C) 2013 Citrix Systems
> > + *
> > + * Author: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > + */
> > +
> > +#include <linux/export.h>
> > +#include <linux/jump_label.h>
> > +#include <linux/types.h>
> > +#include <asm/paravirt.h>
> > +
> > +struct static_key paravirt_steal_enabled;
> > +struct static_key paravirt_steal_rq_enabled;
> > +
> > +struct pv_time_ops pv_time_ops;
> > +EXPORT_SYMBOL_GPL(pv_time_ops);
> > -- 
> > 1.7.10.4
> > 
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