Re: Stolen and degraded time and schedulers

[Jeremy Fitzhardinge]

Dan Hecht wrote:
> Sounds good.  I don't see this in your patchset you sent yesterday
> though; did you add it after sending out those patches?

Yes.

>   if so, could you forward the new patch?  does it explicitly prevent
> stolen time from getting accounted as  user/system time or does it
> just rely on NO_HZ mode sort of happening to work that way (since the
> one shot timer is skipped ahead for missed ticks)?

Hm, not sure.  It doesn't care how often it gets called; it just
accumulates results up to that point, but I'm not sure if the time would
get double accounted.  Perhaps it doesn't matter when using
xen_sched_clock().

Did the get_scheduled_time -> sched_clock make sense to you?

    J
Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Cc: john stultz <johnstul@xxxxxxxxxx>

---
 arch/i386/xen/time.c |  101 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)

===================================================================
--- a/arch/i386/xen/time.c
+++ b/arch/i386/xen/time.c
@@ -2,6 +2,7 @@
 #include <linux/interrupt.h>
 #include <linux/clocksource.h>
 #include <linux/clockchips.h>
+#include <linux/kernel_stat.h>
 
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
@@ -14,6 +15,7 @@
 
 #define XEN_SHIFT 22
 #define TIMER_SLOP	100000	/* Xen may fire a timer up to this many ns early */
+#define NS_PER_TICK	(1000000000ll / HZ)
 
 static DEFINE_PER_CPU(struct clock_event_device, xen_clock_events);
 
@@ -28,6 +30,99 @@ struct shadow_time_info {
 
 static DEFINE_PER_CPU(struct shadow_time_info, shadow_time);
 
+/* runstate info updated by Xen */
+static DEFINE_PER_CPU(struct vcpu_runstate_info, runstate);
+
+/* snapshots of runstate info */
+static DEFINE_PER_CPU(struct vcpu_runstate_info, runstate_snapshot);
+
+/* unused ns of stolen and blocked time */
+static DEFINE_PER_CPU(u64, residual_stolen);
+static DEFINE_PER_CPU(u64, residual_blocked);
+
+/*
+   Runstate accounting
+ */
+static void get_runstate_snapshot(struct vcpu_runstate_info *res)
+{
+	u64 state_time;
+	struct vcpu_runstate_info *state;
+
+	preempt_disable();
+
+	state = &__get_cpu_var(runstate);
+
+	do {
+		state_time = state->state_entry_time;
+		barrier();
+		*res = *state;
+		barrier();
+	} while(state->state_entry_time != state_time);
+
+	preempt_enable();
+}
+
+static void setup_runstate_info(void)
+{
+	struct vcpu_register_runstate_memory_area area;
+
+	area.addr.v = &__get_cpu_var(runstate);
+
+	if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
+			       smp_processor_id(), &area))
+		BUG();
+
+	get_runstate_snapshot(&__get_cpu_var(runstate_snapshot));
+}
+
+static void do_stolen_accounting(void)
+{
+	struct vcpu_runstate_info state;
+	struct vcpu_runstate_info *snap;
+	u64 blocked, runnable, offline, stolen;
+	cputime_t ticks;
+
+	get_runstate_snapshot(&state);
+
+	WARN_ON(state.state != RUNSTATE_running);
+
+	snap = &__get_cpu_var(runstate_snapshot);
+
+	/* work out how much time the VCPU has not been runn*ing*  */
+	blocked = state.time[RUNSTATE_blocked] - snap->time[RUNSTATE_blocked];
+	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.  Passing NULL to
+	   account_steal_time accounts the time as stolen. */
+	stolen = runnable + offline + __get_cpu_var(residual_stolen);
+	ticks = 0;
+	while(stolen >= NS_PER_TICK) {
+		ticks++;
+		stolen -= NS_PER_TICK;
+	}
+	__get_cpu_var(residual_stolen) = stolen;
+	account_steal_time(NULL, ticks);
+
+	/* Add the appropriate number of ticks of blocked time,
+	   including any left-overs from last time.  Passing idle to
+	   account_steal_time accounts the time as idle/wait. */
+	blocked += __get_cpu_var(residual_blocked);
+	ticks = 0;
+	while(blocked >= NS_PER_TICK) {
+		ticks++;
+		blocked -= NS_PER_TICK;
+	}
+	__get_cpu_var(residual_blocked) = blocked;
+	account_steal_time(idle_task(smp_processor_id()), ticks);
+}
+
+
+
+/* Get the CPU speed from Xen */
 unsigned long xen_cpu_khz(void)
 {
 	u64 cpu_khz = 1000000ULL << 32;
@@ -264,6 +359,8 @@ static irqreturn_t xen_timerop_timer_int
 		ret = IRQ_HANDLED;
 	}
 
+	do_stolen_accounting();
+
 	return ret;
 }
 
@@ -338,6 +435,8 @@ static irqreturn_t xen_vcpuop_timer_inte
 		ret = IRQ_HANDLED;
 	}
 
+	do_stolen_accounting();
+
 	return ret;
 }
 
@@ -380,6 +479,8 @@ static void xen_setup_timer(int cpu)
 	evt->cpumask = cpumask_of_cpu(cpu);
 	evt->irq = irq;
 	clockevents_register_device(evt);
+
+	setup_runstate_info();
 
 	put_cpu_var(xen_clock_events);
 }
Subject: Implement xen_sched_clock

Implement xen_sched_clock, which returns the number of ns the current
vcpu has been actually in the running state (vs blocked,
runnable-but-not-running, or offline) since boot.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Cc: john stultz <johnstul@xxxxxxxxxx>

---
 arch/i386/xen/enlighten.c |    2 +-
 arch/i386/xen/time.c      |   14 ++++++++++++++
 arch/i386/xen/xen-ops.h   |    1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

===================================================================
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -664,7 +664,7 @@ static const struct paravirt_ops xen_par
 	.set_wallclock = xen_set_wallclock,
 	.get_wallclock = xen_get_wallclock,
 	.get_cpu_khz = xen_cpu_khz,
-	.get_scheduled_cycles = native_read_tsc,
+	.sched_clock = xen_sched_clock,
 
 #ifdef CONFIG_X86_LOCAL_APIC
 	.apic_write = paravirt_nop,
===================================================================
--- a/arch/i386/xen/time.c
+++ b/arch/i386/xen/time.c
@@ -16,6 +16,8 @@
 #define XEN_SHIFT 22
 #define TIMER_SLOP	100000	/* Xen may fire a timer up to this many ns early */
 #define NS_PER_TICK	(1000000000ll / HZ)
+
+static cycle_t xen_clocksource_read(void);
 
 static DEFINE_PER_CPU(struct clock_event_device, xen_clock_events);
 
@@ -120,6 +122,18 @@ static void do_stolen_accounting(void)
 	account_steal_time(idle_task(smp_processor_id()), ticks);
 }
 
+/* Xen sched_clock implementation.  Returns the number of RUNNING ns */
+unsigned long long xen_sched_clock(void)
+{
+	struct vcpu_runstate_info state;
+	cycle_t now = xen_clocksource_read();
+
+	get_runstate_snapshot(&state);
+
+	WARN_ON(state.state != RUNSTATE_running);
+
+	return state.time[RUNSTATE_running] + (now - state.state_entry_time);
+}
 
 
 /* Get the CPU speed from Xen */
===================================================================
--- a/arch/i386/xen/xen-ops.h
+++ b/arch/i386/xen/xen-ops.h
@@ -14,6 +14,7 @@ void __init xen_time_init(void);
 void __init xen_time_init(void);
 unsigned long xen_get_wallclock(void);
 int xen_set_wallclock(unsigned long time);
+unsigned long long xen_sched_clock(void);
 
 void xen_mark_init_mm_pinned(void);