Messages in this thread | | | Date | Fri, 12 Mar 2004 13:52:09 -0800 | From | Jonathan Lundell <> | Subject | Re: nmi oddity |
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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/
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