Commit f91a8b44 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Jeremy Fitzhardinge
Browse files

xen: Account for stolen time



This patch accounts for the time stolen from our VCPUs.  Stolen time is
time where a vcpu is runnable and could be running, but all available
physical CPUs are being used for something else.

This accounting gets run on each timer interrupt, just as a way to get
it run relatively often, and when interesting things are going on.
Stolen time is not really used by much in the kernel; it is reported
in /proc/stats, and that's about it.
Signed-off-by: default avatarJeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: default avatarChris Wright <chrisw@sous-sol.org>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
parent 9a4029fd
......@@ -11,6 +11,7 @@
#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>
......@@ -25,6 +26,7 @@
/* Xen may fire a timer up to this many ns early */
#define TIMER_SLOP 100000
#define NS_PER_TICK (1000000000LL / HZ)
/* These are perodically updated in shared_info, and then copied here. */
struct shadow_time_info {
......@@ -37,6 +39,139 @@ 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);
/* return an consistent snapshot of 64-bit time/counter value */
static u64 get64(const u64 *p)
{
u64 ret;
if (BITS_PER_LONG < 64) {
u32 *p32 = (u32 *)p;
u32 h, l;
/*
* Read high then low, and then make sure high is
* still the same; this will only loop if low wraps
* and carries into high.
* XXX some clean way to make this endian-proof?
*/
do {
h = p32[1];
barrier();
l = p32[0];
barrier();
} while (p32[1] != h);
ret = (((u64)h) << 32) | l;
} else
ret = *p;
return ret;
}
/*
* 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);
/*
* The runstate info is always updated by the hypervisor on
* the current CPU, so there's no need to use anything
* stronger than a compiler barrier when fetching it.
*/
do {
state_time = get64(&state->state_entry_time);
barrier();
*res = *state;
barrier();
} while (get64(&state->state_entry_time) != state_time);
preempt_enable();
}
static void setup_runstate_info(int cpu)
{
struct vcpu_register_runstate_memory_area area;
area.addr.v = &per_cpu(runstate, cpu);
if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
cpu, &area))
BUG();
}
static void do_stolen_accounting(void)
{
struct vcpu_runstate_info state;
struct vcpu_runstate_info *snap;
s64 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);
if (stolen < 0)
stolen = 0;
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);
if (blocked < 0)
blocked = 0;
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;
......@@ -56,13 +191,11 @@ unsigned long xen_cpu_khz(void)
* Reads a consistent set of time-base values from Xen, into a shadow data
* area.
*/
static void get_time_values_from_xen(void)
static unsigned get_time_values_from_xen(void)
{
struct vcpu_time_info *src;
struct shadow_time_info *dst;
preempt_disable();
/* src is shared memory with the hypervisor, so we need to
make sure we get a consistent snapshot, even in the face of
being preempted. */
......@@ -79,7 +212,7 @@ static void get_time_values_from_xen(void)
rmb(); /* test version after fetching data */
} while ((src->version & 1) | (dst->version ^ src->version));
preempt_enable();
return dst->version;
}
/*
......@@ -123,7 +256,7 @@ static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
static u64 get_nsec_offset(struct shadow_time_info *shadow)
{
u64 now, delta;
rdtscll(now);
now = native_read_tsc();
delta = now - shadow->tsc_timestamp;
return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
}
......@@ -132,10 +265,14 @@ cycle_t xen_clocksource_read(void)
{
struct shadow_time_info *shadow = &get_cpu_var(shadow_time);
cycle_t ret;
unsigned version;
get_time_values_from_xen();
ret = shadow->system_timestamp + get_nsec_offset(shadow);
do {
version = get_time_values_from_xen();
barrier();
ret = shadow->system_timestamp + get_nsec_offset(shadow);
barrier();
} while (version != __get_cpu_var(xen_vcpu)->time.version);
put_cpu_var(shadow_time);
......@@ -352,6 +489,8 @@ static irqreturn_t xen_timer_interrupt(int irq, void *dev_id)
ret = IRQ_HANDLED;
}
do_stolen_accounting();
return ret;
}
......@@ -378,6 +517,8 @@ static void xen_setup_timer(int cpu)
evt->irq = irq;
clockevents_register_device(evt);
setup_runstate_info(cpu);
put_cpu_var(xen_clock_events);
}
......@@ -390,7 +531,7 @@ __init void xen_time_init(void)
clocksource_register(&xen_clocksource);
if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL) == 0) {
/* Successfully turned off 100hz tick, so we have the
/* Successfully turned off 100Hz tick, so we have the
vcpuop-based timer interface */
printk(KERN_DEBUG "Xen: using vcpuop timer interface\n");
xen_clockevent = &xen_vcpuop_clockevent;
......
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