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    Subject[PATCH 03/10] xen: yield to IPI target if necessary
    When sending a call-function IPI to a vcpu, yield if the vcpu isn't
    running.

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

    ---
    arch/i386/xen/smp.c | 14 ++++++++++----
    arch/i386/xen/time.c | 6 ++++++
    arch/i386/xen/xen-ops.h | 2 ++
    3 files changed, 18 insertions(+), 4 deletions(-)

    ===================================================================
    --- a/arch/i386/xen/smp.c
    +++ b/arch/i386/xen/smp.c
    @@ -360,7 +360,8 @@ int xen_smp_call_function_mask(cpumask_t
    void *info, int wait)
    {
    struct call_data_struct data;
    - int cpus;
    + int cpus, cpu;
    + bool yield;

    /* Holding any lock stops cpus from going down. */
    spin_lock(&call_lock);
    @@ -389,9 +390,14 @@ int xen_smp_call_function_mask(cpumask_t
    /* Send a message to other CPUs and wait for them to respond */
    xen_send_IPI_mask(mask, XEN_CALL_FUNCTION_VECTOR);

    - /* Make sure other vcpus get a chance to run.
    - XXX too severe? Maybe we should check the other CPU's states? */
    - HYPERVISOR_sched_op(SCHEDOP_yield, 0);
    + /* Make sure other vcpus get a chance to run if they need to. */
    + yield = false;
    + for_each_cpu_mask(cpu, mask)
    + if (xen_vcpu_stolen(cpu))
    + yield = true;
    +
    + if (yield)
    + HYPERVISOR_sched_op(SCHEDOP_yield, 0);

    /* Wait for response */
    while (atomic_read(&data.started) != cpus ||
    ===================================================================
    --- a/arch/i386/xen/time.c
    +++ b/arch/i386/xen/time.c
    @@ -103,6 +103,12 @@ static void get_runstate_snapshot(struct
    *res = *state;
    barrier();
    } while (get64(&state->state_entry_time) != state_time);
    +}
    +
    +/* return true when a vcpu could run but has no real cpu to run on */
    +bool xen_vcpu_stolen(int vcpu)
    +{
    + return per_cpu(runstate, vcpu).state == RUNSTATE_runnable;
    }

    static void setup_runstate_info(int cpu)
    ===================================================================
    --- a/arch/i386/xen/xen-ops.h
    +++ b/arch/i386/xen/xen-ops.h
    @@ -27,6 +27,8 @@ int xen_set_wallclock(unsigned long time
    int xen_set_wallclock(unsigned long time);
    unsigned long long xen_sched_clock(void);

    +bool xen_vcpu_stolen(int vcpu);
    +
    void xen_mark_init_mm_pinned(void);

    DECLARE_PER_CPU(enum paravirt_lazy_mode, xen_lazy_mode);
    --

    -
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