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    SubjectRe: [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@gmail.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@gmail.com>
    > Cc: Peter Zijlstra <a.p.zijlstra@chello.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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