Re: [PATCH] fix get_jiffies_64 to work on voyager

[Tim Schmielau]

On Tue, 6 Jan 2004, Andrew Morton wrote:

> James Bottomley <James.Bottomley@xxxxxxxxxxxx> wrote:
> >
> > This patch
> > 
> > 
> >  ChangeSet@xxxxxxxxxx, 2003-12-30 15:40:23-08:00, akpm@xxxxxxxx
> >    [PATCH] ia32 jiffy wrapping fixes
> > 
> >  Causes the voyager boot to hang.  The problem is this change:
> > 
> >  --- a/arch/i386/kernel/timers/timer_tsc.c       Tue Jan  6 09:57:34 2004
> >  +++ b/arch/i386/kernel/timers/timer_tsc.c       Tue Jan  6 09:57:34 2004
> >  @@ -141,7 +140,7 @@
> >   #ifndef CONFIG_NUMA
> >          if (!use_tsc)
> >   #endif
> >  -               return (unsigned long long)jiffies * (1000000000 / HZ);
> >  +               return (unsigned long long)get_jiffies_64() *
> >  (1000000000 / HZ);
> 
> Hm, OK.  I hit the same deadlock when running with the "don't require TSCs
> to be synchronised in sched_clock()" patch from -mm.  The fix for that is
> below.  I shall accelerate it.
> 
> --- 25/arch/i386/kernel/timers/timer_tsc.c~sched_clock-2.6.0-A1-deadlock-fix	2003-12-30 00:45:09.000000000 -0800
> +++ 25-akpm/arch/i386/kernel/timers/timer_tsc.c	2003-12-30 00:45:09.000000000 -0800
> @@ -140,7 +140,8 @@ unsigned long long sched_clock(void)
>  #ifndef CONFIG_NUMA
>  	if (!use_tsc)
>  #endif
> -		return (unsigned long long)get_jiffies_64() * (1000000000 / HZ);
> +		/* jiffies might overflow but this is not a big deal here */
> +		return (unsigned long long)jiffies * (1000000000 / HZ);
>  
>  	/* Read the Time Stamp Counter */
>  	rdtscll(this_offset);

Yes, please revert that change. When I tested it, I didn't realize I need 
NUMA or clear use_tsc to actually cover the change. And it's indeed not a 
big deal.

The proposed get_jiffies_64() change however looks quite fragile to me.

Sorry,
Tim
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