lkml.org 
[lkml]   [2004]   [Mar]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: nmi oddity
    At 12:13 PM +0100 3/11/04, Mikael Pettersson wrote:
    >Jonathan Lundell writes:
    > > Running smp 2.4.9 (don't ask) with updated nmi logic on a Dell 650
    > > (UP P4), I notice that NMI is running at about 1.08 Hz. Per the
    > > kernel logic, it should be running at HZ (100) Hz.
    > >
    > > I'm using NMI_LOCAL_APIC. check_nmi_watchdog() never gets called in
    > > this mode in an smp kernel, near as I can tell, so nmi_hz never gets
    > > set to 1.
    > >
    > > What's going on? Or does anyone else see it?
    >
    >This is a normal. The NMIs are generated from an in-CPU performance
    >counter configured to increment once per CPU core clock cycle.
    >(There is no wallclock-like event available, alas.)
    >
    >Whenever the kernel is idle, "hlt" is normally executed which
    >stops the CPU until the next external interrupt (typically the
    >timer). Hence, an idle machine will see a much lower NMI frequence
    >than a non-idle one.

    That's exactly what's happening; thanks.

    If I run a compute-intensive task in the background (eg cat
    /dev/zero > /dev/null), the nmi frequency jumps up to 100 Hz.

    Switching to NMI_IO_APIC is the best solution for me.

    It makes NMI_LOCAL_APIC a v. questionable choice for a watchdog....

    >This behaviour is not universal. Server Tualatins seem to run at
    >full speed all the time; perhaps they ignore hlt?
    >
    >If you want NMI_LOCAL_APIC to be clock-like, upgrade your cooling
    >solution and disable hlt.
    >
    >/Mikael
    >-
    >To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    >the body of a message to majordomo@vger.kernel.org
    >More majordomo info at http://vger.kernel.org/majordomo-info.html
    >Please read the FAQ at http://www.tux.org/lkml/


    --
    /Jonathan Lundell.
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 14:01    [W:5.252 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site