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    Hi all,

    These 2 patches try to fix the "perf top" soft lockups under Xen
    reported by Steven at: https://lkml.org/lkml/2012/2/9/506

    I tested it with 3.4-rc2 and "perf top" works well now.

    Steven,
    Could you please help to test it too?

    The soft lockup code path is:

    __irq_work_queue
    arch_irq_work_raise
    apic->send_IPI_self(IRQ_WORK_VECTOR);
    apic_send_IPI_self
    __default_send_IPI_shortcut
    __xapic_wait_icr_idle

    static inline void __xapic_wait_icr_idle(void)
    {
    while (native_apic_mem_read(APIC_ICR) & APIC_ICR_BUSY)
    cpu_relax();
    }

    The lockup happens at above while looop.

    The cause is that Xen has not implemented the APIC IPI interface yet.
    Xen has IPI interface: xen_send_IPI_one, but it's only used in
    xen_smp_send_reschedule, xen_smp_send_call_function_ipi and
    xen_smp_send_call_function_single_ipi, etc.

    So we need to implement Xen's APIC IPI interface as Ben's patch does.
    And implement Xen's IRQ_WORK_VECTOR handler.

    Ben Guthro (1):
    xen: implement apic ipi interface

    Lin Ming (1):
    xen: implement IRQ_WORK_VECTOR handler

    arch/x86/include/asm/xen/events.h | 1 +
    arch/x86/xen/enlighten.c | 7 ++
    arch/x86/xen/smp.c | 111 +++++++++++++++++++++++++++++++++++-
    arch/x86/xen/smp.h | 12 ++++
    4 files changed, 127 insertions(+), 4 deletions(-)

    Any comment is appreciated.
    Lin Ming



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