linux-kernel - Re: [PATCH] documentation: nmi_watchdog=2 works on x86_64 (was: 2.6.25-rc: complete lockup on boot/start of X (bisected))

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Date:	Sun, 23 Mar 2008 13:15:50 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Marcin Slusarz" <marcin.slusarz@...il.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] documentation: nmi_watchdog=2 works on x86_64 (was: 2.6.25-rc: complete lockup on boot/start of X (bisected))

On Sun, Mar 23, 2008 at 1:06 PM, Marcin Slusarz
<marcin.slusarz@...il.com> wrote:
> On Sun, Mar 23, 2008 at 08:06:08PM +0100, Peter Zijlstra wrote:
>  > On Sun, 2008-03-23 at 19:46 +0100, Marcin Slusarz wrote:
>  >
>  > > 4 different lockups:
>  > > http://alan.umcs.lublin.pl/~mslusarz/kernel/2008.03.23-lockup/
>  >
>  > Brilliant, these are extremely helpful.
>  >
>  > What seems to happen is a classic xtime deadlock, doing a xtime
>  > seq_readlock while holding a seq_writelock.
>  >
>  > Only need to figure out _why_ that is happening....
>  >
>  > > Are there any downsides of using nmi_watchdog=2 all the time?
>  >
>  > Some machines are said to not boot due to NMIs, hence the default is
>  > off, but afaik, _if_ it works there are no downsides aside from the
>  > slight NMI handling overhead.
>  >
>  > > ps: Documentation/nmi_watchdog.txt says: "Currently, local APIC mode
>  > > (nmi_watchdog=2) does not work on x86-64.". It's not true, so maybe someone
>  > > should update this file?
>  >
>  > Care to send a patch to the x86 maintainers? :-)
>  >
>
>  ---
>  documentation: nmi_watchdog=2 works on x86_64
>
>  Signed-off-by: Marcin Slusarz <marcin.slusarz@...il.com>
>  Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>  ---
>   Documentation/nmi_watchdog.txt |    3 +--
>   1 files changed, 1 insertions(+), 2 deletions(-)
>
>  diff --git a/Documentation/nmi_watchdog.txt b/Documentation/nmi_watchdog.txt
>  index c025a45..757c729 100644
>  --- a/Documentation/nmi_watchdog.txt
>  +++ b/Documentation/nmi_watchdog.txt
>  @@ -23,8 +23,7 @@ kernel debugging options, such as Kernel Stack Meter or Kernel Tracer,
>   may implicitly disable the NMI watchdog.]
>
>   For x86-64, the needed APIC is always compiled in, and the NMI watchdog is
>  -always enabled with I/O-APIC mode (nmi_watchdog=1). Currently, local APIC
>  -mode (nmi_watchdog=2) does not work on x86-64.
>  +always enabled with I/O-APIC mode (nmi_watchdog=1).
>
>   Using local APIC (nmi_watchdog=2) needs the first performance register, so
>   you can't use it for other purposes (such as high precision performance
>  --
anyone has nmi_watchdog=1 works on x86_64 with amd platform?

or nmi_watchdog=1 only works with intel box?

maybe we can default that to different value according to different
cpu vendor...

YH
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