Re: Stolen and degraded time and schedulers
From: Dan Hecht
Date: Wed Mar 14 2007 - 16:47:26 EST
On 03/14/2007 01:31 PM, Jeremy Fitzhardinge wrote:
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().
I think you might be double counting time in some cases. sched_clock()
isn't really relevant to stolen time accounting (i.e. cpustat->steal).
I think what you want is to make sure that the sum of the cputime passed
to all of:
account_user_time
account_system_time
account_steal_time
adds up to the total amount of time that has passed. I think it is sort
of working for you (i.e. doesn't always double count stolen ticks) since
in NO_HZ mode, update_process_time (which calls account_user_time &
account_system_time) happens to be skipped during periods of stolen time
due to the hrtimer_forward()'ing of the one shot expiry.
Did the get_scheduled_time -> sched_clock make sense to you?
The get_scheduled_time change should work fine for vmi.
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);
-
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