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SubjectRe: [PATCH] fix get_jiffies_64 to work on voyager
On Tue, 6 Jan 2004, Andrew Morton wrote:

> James Bottomley <James.Bottomley@SteelEye.com> wrote:
> >
> > This patch
> >
> >
> > ChangeSet@1.1534.5.2, 2003-12-30 15:40:23-08:00, akpm@osdl.org
> > [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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