Re: Measuring tools - top and interrupts

[Björn Steinbrink]

On 2006.06.24 08:26:23 +0200, Mike Galbraith wrote:
> On Sat, 2006-06-24 at 07:59 +0200, Mike Galbraith wrote:
> > On Thu, 2006-06-22 at 09:58 -0700, Danial Thom wrote:
> > 
> > > And 75K pps may not be "much", but its still at
> > > least 10% of what the system can handle, so it
> > > should measure around a 10% load. 2.4 measures
> > > about 12% load. So the only conclusion is that
> > > load accounting is broken in 2.6.
> > 
> > For UP, yes.  SMP kernel accounts irq processing time properly.

Do you actually see 100% idle? On both, UP and SMP, I see non-zero hi/si
values using "top". With IO-APIC enabled, I see only non-zero si values
for my tg3 NICs, and non-zero hi and si values for the nVidia NIC. With
IO-APIC disabled, I also see a non-zero hi value for the tg3 on UP,
guess that's normal... But I never see 100% idle while flooding the box
with pings.

> For my little box, the below cures it.
> 
> --- linux-2.6.17x/arch/i386/kernel/apic.c.org	2006-06-24 08:08:46.000000000 +0200
> +++ linux-2.6.17x/arch/i386/kernel/apic.c	2006-06-24 08:09:16.000000000 +0200
> @@ -1175,9 +1175,7 @@ EXPORT_SYMBOL(switch_ipi_to_APIC_timer);
>  inline void smp_local_timer_interrupt(struct pt_regs * regs)
>  {
>  	profile_tick(CPU_PROFILING, regs);
> -#ifdef CONFIG_SMP
>  	update_process_times(user_mode_vm(regs));
> -#endif
>  
>  	/*
>  	 * We take the 'long' return path, and there every subsystem

The non-SMP call to update_process_times() is in do_timer_interrupt_hook(),
so I guess the above is not the Right Thing to do. I don't even see how
you could reach smp_local_timer_interrupt() without going through
do_timer_interrupt_hook() first.

Björn
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