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

From: Stefano Stabellini
Date: Fri Nov 20 2015 - 09:31:35 EST


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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