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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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