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Subject[PATCH v2 0/2] fix "perf top" soft lockups under Xen
Date
v2: 
- fix compile issues if no CONFIG_SMP, Konrad Rzeszutek Wilk
- move inc_irq_stat after irq_work_run

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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