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    Subject[PATCH 15/25] xen: xen time fixups
    1. make sure timer state is set up before bringing up CPU
    2. make sure snapshot of 64-bit time values is atomic

    Be sure, however, that the clockevent source is registered on its home
    CPU.

    Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>

    ---
    arch/i386/xen/smp.c | 4 +-
    arch/i386/xen/time.c | 93 +++++++++++++++++++++++++++++++----------------
    arch/i386/xen/xen-ops.h | 3 +
    3 files changed, 67 insertions(+), 33 deletions(-)

    ===================================================================
    --- a/arch/i386/xen/smp.c
    +++ b/arch/i386/xen/smp.c
    @@ -78,10 +78,11 @@ static __cpuinit void cpu_bringup_and_id
    int cpu = smp_processor_id();

    cpu_init();
    - xen_setup_timer();

    preempt_disable();
    per_cpu(cpu_state, cpu) = CPU_ONLINE;
    +
    + xen_setup_cpu_clockevents();

    /* We can take interrupts now: we're officially "up". */
    local_irq_enable();
    @@ -275,6 +276,7 @@ int __cpuinit xen_cpu_up(unsigned int cp
    per_cpu(current_task, cpu) = idle;
    xen_vcpu_setup(cpu);
    irq_ctx_init(cpu);
    + xen_setup_timer(cpu);

    /* make sure interrupts start blocked */
    per_cpu(xen_vcpu, cpu)->evtchn_upcall_mask = 1;
    ===================================================================
    --- a/arch/i386/xen/time.c
    +++ b/arch/i386/xen/time.c
    @@ -40,6 +40,35 @@ static DEFINE_PER_CPU(u64, residual_stol
    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
    */
    @@ -53,24 +82,22 @@ static void get_runstate_snapshot(struct
    state = &__get_cpu_var(runstate);

    do {
    - state_time = state->state_entry_time;
    + state_time = get64(&state->state_entry_time);
    barrier();
    *res = *state;
    barrier();
    - } while(state->state_entry_time != state_time);
    -}
    -
    -static void setup_runstate_info(void)
    + } while(get64(&state->state_entry_time) != state_time);
    +}
    +
    +static void setup_runstate_info(int cpu)
    {
    struct vcpu_register_runstate_memory_area area;

    - area.addr.v = &__get_cpu_var(runstate);
    + area.addr.v = &per_cpu(runstate, cpu);

    if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
    - smp_processor_id(), &area))
    + cpu, &area))
    BUG();
    -
    - get_runstate_snapshot(&__get_cpu_var(runstate_snapshot));
    }

    static void do_stolen_accounting(void)
    @@ -185,12 +212,10 @@ 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);
    @@ -205,7 +230,7 @@ static void get_time_values_from_xen(voi
    rmb();
    } while ((src->version & 1) | (dst->version ^ src->version));

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

    /*
    @@ -249,7 +274,7 @@ 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);
    }
    @@ -258,10 +283,14 @@ static 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);

    @@ -483,9 +512,8 @@ static irqreturn_t xen_timer_interrupt(i
    return ret;
    }

    -void xen_setup_timer(void)
    -{
    - int cpu = smp_processor_id();
    +void xen_setup_timer(int cpu)
    +{
    const char *name;
    struct clock_event_device *evt;
    int irq;
    @@ -500,23 +528,25 @@ void xen_setup_timer(void)
    IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
    name, NULL);

    - evt = &get_cpu_var(xen_clock_events);
    + evt = &per_cpu(xen_clock_events, cpu);
    memcpy(evt, xen_clockevent, sizeof(*evt));

    evt->cpumask = cpumask_of_cpu(cpu);
    evt->irq = irq;
    - clockevents_register_device(evt);
    -
    - setup_runstate_info();
    -
    - put_cpu_var(xen_clock_events);
    +
    + setup_runstate_info(cpu);
    +}
    +
    +void xen_setup_cpu_clockevents(void)
    +{
    + BUG_ON(preemptible());
    +
    + clockevents_register_device(&__get_cpu_var(xen_clock_events));
    }

    __init void xen_time_init(void)
    {
    int cpu = smp_processor_id();
    -
    - get_time_values_from_xen();

    clocksource_register(&xen_clocksource);

    @@ -534,5 +564,6 @@ __init void xen_time_init(void)

    tsc_disable = 0;

    - xen_setup_timer();
    -}
    + xen_setup_timer(cpu);
    + xen_setup_cpu_clockevents();
    +}
    ===================================================================
    --- a/arch/i386/xen/xen-ops.h
    +++ b/arch/i386/xen/xen-ops.h
    @@ -25,7 +25,8 @@ unsigned long xen_get_wallclock(void);
    unsigned long xen_get_wallclock(void);
    int xen_set_wallclock(unsigned long time);
    unsigned long long xen_sched_clock(void);
    -void xen_setup_timer(void);
    +void xen_setup_timer(int cpu);
    +void xen_setup_cpu_clockevents(void);

    void xen_mark_init_mm_pinned(void);

    --

    -
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