linux-kernel - Re: [PATCH v2 0/2] fix "perf top" soft lockups under Xen

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Date:	Fri, 20 Apr 2012 12:21:34 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Lin Ming <mlin@...pku.edu.cn>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Noonan <steven@...inklabs.net>,
	Ben Guthro <ben@...hro.net>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Marcus Granado <marcus.granado@...rix.com>,
	xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org
Subject: Re: [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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