Re: Linux 2.6.21-rc1

[Daniel Walker]

On Tue, 2007-02-20 at 20:53 -0800, Linus Torvalds wrote:
> Ok, the merge window for 2.6.21 has closed, and -rc1 is out there.
> 
> There's a lot of changes, as is usual for an -rc1 thing, but at least so 
> far it would seem that 2.6.20 has been a good base, and I don't think we 
> have anything *really* scary here.
> 
> The most interesting core change may be the dyntick/nohz one, where timer 
> ticks will only happen when needed. It's been brewing for a _loong_ time, 
> but it's in the standard kernel now as an option. 

On i386 I get the following,

TCP cubic registered                                                            
NET: Registered protocol family 1                                               
NET: Registered protocol family 17                                              
Testing NMI watchdog ... CPU#0: NMI appears to be stuck (24->24)!               
CPU#1: NMI appears to be stuck (0->0)!                                          
CPU#2: NMI appears to be stuck (0->0)!                                          
CPU#3: NMI appears to be stuck (0->0)!              

when I add nmi_watchdog=1 to my boot args which worked on prior kernels.
On closer inspection it looks like arch/i386/kernel/io_apic.c :
check_timer() --> timer_irq_works() depends on IRQ0 incrementing jiffies
which is no longer the case AFAIK.

I'm not sure exactly how that relates to the NMI, but the check_timer()
function disabled the NMI through the io-apic if it can't get the
"timer" working through the io-apic.

Daniel

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