Re: Ktimer / -rt9 (+custom) monotonic_clock going backwards.

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 20 Oct 2005, Steven Rostedt wrote:

>
> On Thu, 20 Oct 2005, Ingo Molnar wrote:
>
> >
> > * Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > > static inline nsec_t __get_nsec_offset(void)
> > > {
> > > 	cycle_t cycle_now, cycle_delta;
> > > 	nsec_t ns_offset;
> > >
> > > 	/* read clocksource */
> > > 	cycle_now = read_clocksource(clock);
> > >
> > > 	/* calculate the delta since the last timeofday_periodic_hook */
> > > 	cycle_delta = (cycle_now - cycle_last) & clock->mask;
> > >
> > > 	/* convert to nanoseconds */
> > > 	ns_offset = cyc2ns(clock, ntp_adj, cycle_delta);
> > >
> > > 	/* Special case for jiffies tick/offset based systems
> > > 	 * add arch specific offset
> > > 	 */
> > > 	ns_offset += arch_getoffset();
> > >
> > > 	return ns_offset;
> > > }
> > >
> > > cycle_now is 32 bits.  If the clocksource overflows (which it can in
> > > 30 seconds) the cyclec_delta will be wrong.
> >
> > isnt cycle_t 64 bits?
> >
>
> Not anymore.
>
> include/linux/time.h:
>
> /* timeofday base types */
> typedef s64 nsec_t;
> typedef unsigned long cycle_t;
>

FYI,

I just switched cycle_t to u64 and hackbench no longer makes the time go
backwards.

John, would this cause any problems to keep cycle_t at s64?

-- Steve