Re: [PATCH v3] xen: add steal_clock support on x86

From: Stefano Stabellini
Date: Thu May 19 2016 - 13:15:36 EST

On Thu, 19 May 2016, Juergen Gross wrote:
> The pv_time_ops structure contains a function pointer for the
> "steal_clock" functionality used only by KVM and Xen on ARM. Xen on x86
> uses its own mechanism to account for the "stolen" time a thread wasn't
> able to run due to hypervisor scheduling.
>
> Add support in Xen arch independent time handling for this feature by
> moving it out of the arm arch into drivers/xen and remove the x86 Xen
> hack.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V3: add #include <asm/paravirt.h> to avoid build error on arm
> V2: remove the x86 do_stolen_accounting() hack
> ---
> arch/arm/xen/enlighten.c | 17 ++---------------
> arch/x86/xen/time.c | 44 ++------------------------------------------
> drivers/xen/time.c | 20 ++++++++++++++++++++
> include/linux/kernel_stat.h | 1 -
> include/xen/xen-ops.h | 1 +
> kernel/sched/cputime.c | 10 ----------
> 6 files changed, 25 insertions(+), 68 deletions(-)
>
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 75cd734..9163b94 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -84,19 +84,6 @@ int xen_unmap_domain_gfn_range(struct vm_area_struct *vma,
> }
> EXPORT_SYMBOL_GPL(xen_unmap_domain_gfn_range);
>
> -static unsigned long long xen_stolen_accounting(int cpu)
> -{
> - struct vcpu_runstate_info state;
> -
> - BUG_ON(cpu != smp_processor_id());
> -
> - xen_get_runstate_snapshot(&state);
> -
> - WARN_ON(state.state != RUNSTATE_running);
> -
> - return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
> -}
> -
> static void xen_read_wallclock(struct timespec64 *ts)
> {
> u32 version;
> @@ -355,8 +342,8 @@ static int __init xen_guest_init(void)
>
> register_cpu_notifier(&xen_cpu_notifier);
>
> - pv_time_ops.steal_clock = xen_stolen_accounting;
> - static_key_slow_inc(&paravirt_steal_enabled);
> + xen_time_setup_guest();

You can remove

#include <asm/paravirt.h>

from headers now I believe



> if (xen_initial_domain())
> pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);
>
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index a0a4e55..6be31df 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -11,8 +11,6 @@
> #include <linux/interrupt.h>
> #include <linux/clocksource.h>
> #include <linux/clockchips.h>
> -#include <linux/kernel_stat.h>
> -#include <linux/math64.h>
> #include <linux/gfp.h>
> #include <linux/slab.h>
> #include <linux/pvclock_gtod.h>
> @@ -31,44 +29,6 @@
>
> /* Xen may fire a timer up to this many ns early */
> #define TIMER_SLOP 100000
> -#define NS_PER_TICK (1000000000LL / HZ)
> -
> -/* snapshots of runstate info */
> -static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate_snapshot);
> -
> -/* unused ns of stolen time */
> -static DEFINE_PER_CPU(u64, xen_residual_stolen);
> -
> -static void do_stolen_accounting(void)
> -{
> - struct vcpu_runstate_info state;
> - struct vcpu_runstate_info *snap;
> - s64 runnable, offline, stolen;
> - cputime_t ticks;
> -
> - xen_get_runstate_snapshot(&state);
> -
> - WARN_ON(state.state != RUNSTATE_running);
> -
> - snap = this_cpu_ptr(&xen_runstate_snapshot);
> -
> - /* work out how much time the VCPU has not been runn*ing* */
> - runnable = state.time[RUNSTATE_runnable] - snap->time[RUNSTATE_runnable];
> - offline = state.time[RUNSTATE_offline] - snap->time[RUNSTATE_offline];
> -
> - *snap = state;
> -
> - /* Add the appropriate number of ticks of stolen time,
> - including any left-overs from last time. */
> - stolen = runnable + offline + __this_cpu_read(xen_residual_stolen);
> -
> - if (stolen < 0)
> - stolen = 0;
> -
> - ticks = iter_div_u64_rem(stolen, NS_PER_TICK, &stolen);
> - __this_cpu_write(xen_residual_stolen, stolen);
> - account_steal_ticks(ticks);
> -}
>
> /* Get the TSC speed from Xen */
> static unsigned long xen_tsc_khz(void)
> @@ -335,8 +295,6 @@ static irqreturn_t xen_timer_interrupt(int irq, void *dev_id)
> ret = IRQ_HANDLED;
> }
>
> - do_stolen_accounting();
> -
> return ret;
> }
>
> @@ -431,6 +389,8 @@ static void __init xen_time_init(void)
> xen_setup_timer(cpu);
> xen_setup_cpu_clockevents();
>
> + xen_time_setup_guest();
> +
> if (xen_initial_domain())
> pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);
> }
> diff --git a/drivers/xen/time.c b/drivers/xen/time.c
> index 7107842..2257b66 100644
> --- a/drivers/xen/time.c
> +++ b/drivers/xen/time.c
> @@ -6,6 +6,7 @@
> #include <linux/math64.h>
> #include <linux/gfp.h>
>
> +#include <asm/paravirt.h>
> #include <asm/xen/hypervisor.h>
> #include <asm/xen/hypercall.h>
>
> @@ -75,6 +76,15 @@ bool xen_vcpu_stolen(int vcpu)
> return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
> }
>
> +static u64 xen_steal_clock(int cpu)
> +{
> + struct vcpu_runstate_info state;
> +
> + BUG_ON(cpu != smp_processor_id());
> + xen_get_runstate_snapshot(&state);
> + return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
> +}
> +
> void xen_setup_runstate_info(int cpu)
> {
> struct vcpu_register_runstate_memory_area area;
> @@ -86,3 +96,13 @@ void xen_setup_runstate_info(int cpu)
> BUG();
> }
>
> +void __init xen_time_setup_guest(void)
> +{
> + pv_time_ops.steal_clock = xen_steal_clock;
> +
> + static_key_slow_inc(&paravirt_steal_enabled);
> + /*
> + * We can't set paravirt_steal_rq_enabled as this would require the
> + * capability to read another cpu's runstate info.
> + */
> +}
> diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
> index 25a822f..44fda64 100644
> --- a/include/linux/kernel_stat.h
> +++ b/include/linux/kernel_stat.h
> @@ -92,7 +92,6 @@ static inline void account_process_tick(struct task_struct *tsk, int user)
> extern void account_process_tick(struct task_struct *, int user);
> #endif
>
> -extern void account_steal_ticks(unsigned long ticks);
> extern void account_idle_ticks(unsigned long ticks);
>
> #endif /* _LINUX_KERNEL_STAT_H */
> diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
> index 86abe07..5ce51c2 100644
> --- a/include/xen/xen-ops.h
> +++ b/include/xen/xen-ops.h
> @@ -21,6 +21,7 @@ void xen_resume_notifier_unregister(struct notifier_block *nb);
>
> bool xen_vcpu_stolen(int vcpu);
> void xen_setup_runstate_info(int cpu);
> +void __init xen_time_setup_guest(void);

please avoid __init in headers


> void xen_get_runstate_snapshot(struct vcpu_runstate_info *res);
>
> int xen_setup_shutdown_event(void);
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 75f98c5..8c4c6dc 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -490,16 +490,6 @@ void account_process_tick(struct task_struct *p, int user_tick)
> }
>
> /*
> - * Account multiple ticks of steal time.
> - * @p: the process from which the cpu time has been stolen
> - * @ticks: number of stolen ticks
> - */
> -void account_steal_ticks(unsigned long ticks)
> -{
> - account_steal_time(jiffies_to_cputime(ticks));
> -}
> -
> -/*
> * Account multiple ticks of idle time.
> * @ticks: number of stolen ticks
> */
> --
> 2.6.6
>