RE: ia64 printk_clock()

["Chen, Kenneth W" <kenneth.w.chen@intel.com>]

Luck, Tony wrote on Monday, February 06, 2006 10:14 AM
> On Fri, Feb 03, 2006 at 09:43:29AM -0800, Chen, Kenneth W wrote:
> > Why don't we look at ar.k3, it contains per_cpu base address.
> > If it has a none zero value, then it is initialized by
> > per_cpu_init and is safe to call sched_clock.
> 
> We also need to check whether ar.itc is synchronized on different
> cpus ... if it isn't, then sched_clock() is useless.  Here's a
> simple extension of your patch that does this, falling back to using
> a jiffie based clock (which means you'd only have HZ resolution on
> systems where there is drift).
> 
> If that isn't good enough, then I'd be happy to see a patch that
> does a lockless interpolation.
> 
> diff --git a/arch/ia64/kernel/head.S b/arch/ia64/kernel/head.S
> index fbc7ea3..99cfef8 100644
> --- a/arch/ia64/kernel/head.S
> +++ b/arch/ia64/kernel/head.S
> @@ -352,6 +352,7 @@ start_ap:
>  	mov ar.rsc=0		// place RSE in enforced lazy mode
>  	;;
>  	loadrs			// clear the dirty partition
> +	mov ar.k3=r0		// clear physical per-CPU base
>  	;;
>  	mov ar.bspstore=r2	// establish the new RSE stack
>  	;;

Sorry, I'm the one who is spreading ... can we change this hunk
to use defined kr constant?

diff --git a/arch/ia64/kernel/head.S b/arch/ia64/kernel/head.S
index fbc7ea3..99cfef8 100644
--- a/arch/ia64/kernel/head.S
+++ b/arch/ia64/kernel/head.S
@@ -352,6 +352,7 @@ start_ap:
 	mov ar.rsc=0		// place RSE in enforced lazy mode
 	;;
 	loadrs			// clear the dirty partition
+	mov IA64_KR(PER_CPU_DATA)=r0
 	;;
 	mov ar.bspstore=r2	// establish the new RSE stack
 	;;