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    Subject[patch 19/33] xen: Account for time stolen by Xen
    This patch accounts for the time Xen steals 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: Jeremy Fitzhardinge <jeremy@xensource.com>
    Acked-by: Chris Wright <chrisw@sous-sol.org>
    Cc: john stultz <johnstul@us.ibm.com>
    Cc: Rik van Riel <riel@redhat.com>
    ---
    arch/i386/xen/time.c | 163 ++++++++++++++++++++++++++++++++++++++++++++++----
    1 file changed, 153 insertions(+), 10 deletions(-)

    ===================================================================
    --- a/arch/i386/xen/time.c
    +++ b/arch/i386/xen/time.c
    @@ -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>
    @@ -23,6 +24,7 @@

    #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)

    /* These are perodically updated in shared_info, and then copied here. */
    struct shadow_time_info {
    @@ -35,6 +37,141 @@ 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(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;
    + 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;
    @@ -54,12 +191,10 @@ 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 = &__get_cpu_var(xen_vcpu)->time;
    dst = &__get_cpu_var(shadow_time);
    @@ -74,7 +209,7 @@ static void get_time_values_from_xen(voi
    rmb();
    } while ((src->version & 1) | (dst->version ^ src->version));

    - preempt_enable();
    + return dst->version;
    }

    /*
    @@ -118,7 +253,7 @@ static u64 get_nsec_offset(struct shadow
    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);
    }
    @@ -127,10 +262,14 @@ cycle_t xen_clocksource_read(void)
    {
    struct shadow_time_info *shadow = &get_cpu_var(shadow_time);
    cycle_t ret;
    -
    - get_time_values_from_xen();
    -
    - ret = shadow->system_timestamp + get_nsec_offset(shadow);
    + unsigned version;
    +
    + 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);

    @@ -347,6 +486,8 @@ static irqreturn_t xen_timer_interrupt(i
    ret = IRQ_HANDLED;
    }

    + do_stolen_accounting();
    +
    return ret;
    }

    @@ -373,6 +514,8 @@ static void xen_setup_timer(int cpu)
    evt->irq = irq;
    clockevents_register_device(evt);

    + setup_runstate_info();
    +
    put_cpu_var(xen_clock_events);
    }

    @@ -385,7 +528,7 @@ __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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