[Xen-devel] [PATCH v4] xen: add steal_clock support on x86

[Juergen Gross <jgross@xxxxxxxx>]

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>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
V4: minor adjustments as requested by Stefano Stabellini (remove
    no longer needed #include, remove __init from header)
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    | 18 ++----------------
 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(+), 69 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 75cd734..71db30c 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -12,7 +12,6 @@
 #include <xen/page.h>
 #include <xen/interface/sched.h>
 #include <xen/xen-ops.h>
-#include <asm/paravirt.h>
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
 #include <asm/system_misc.h>
@@ -84,19 +83,6 @@ 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 +341,8 @@ 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();
+
        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..77bf9d1 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 xen_time_setup_guest(void);
 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


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