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    SubjectRe: [PATCH v2 0/2] fix "perf top" soft lockups under Xen
    On Sat, Apr 21, 2012 at 12:11:03AM +0800, Lin Ming wrote:
    > v2:
    > - fix compile issues if no CONFIG_SMP, Konrad Rzeszutek Wilk
    > - move inc_irq_stat after irq_work_run

    They look good to me (and they work nicely - thanks!)
    so putting in the 3.5 queue.

    >
    > These 2 patches fixed the "perf top" soft lockups under Xen
    > reported by Steven at: https://lkml.org/lkml/2012/2/9/506
    >
    > Both Steven and I tested it and "perf top" works well now.
    >
    > 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 | 9 +++
    > arch/x86/xen/smp.c | 111 +++++++++++++++++++++++++++++++++++-
    > arch/x86/xen/smp.h | 12 ++++
    > 4 files changed, 129 insertions(+), 4 deletions(-)


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