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

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Message-ID: <CAF1ivSZqe54_gAQNZW_teiApObkXsC5iu04Siy1OEnm9M9AcUA@mail.gmail.com>
Date:	Sun, 15 Apr 2012 14:14:57 +0800
From:	Lin Ming <mlin@...pku.edu.cn>
To:	linux-kernel@...r.kernel.org
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Steven Noonan <steven@...inklabs.net>,
	Marcus Granado <marcus.granado@...rix.com>,
	xen-devel@...ts.xen.org, Ben Guthro <ben@...hro.net>
Subject: Re: [PATCH 0/2] fix "perf top" soft lockups under Xen

(Forgot mail subject, add it)

On Sun, Apr 15, 2012 at 2:09 PM, Lin Ming <mlin@...pku.edu.cn> wrote:
> 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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