Hi,
On Wed, 21 Jun 2006, john stultz wrote:
> > * @is_continuous: defines if clocksource is free-running.
> > - * @interval_cycles: Used internally by timekeeping core, please ignore.
> > - * @interval_snsecs: Used internally by timekeeping core, please ignore.
> > + * @cycle_interval: Used internally by timekeeping core, please ignore.
> > + * @xtime_interval: Used internally by timekeeping core, please ignore.
> > */
>
> Where the variable name changes really necessary (I find them less
> clear)? You also forgot to add error here as it is added below.
I actually find them more clear this way, cycle values start with cycle_,
xtime related variables start with xtime_ and update intervals end with
_interval, this makes everything quite consistent.
In the middle term I also want to document them properly, so I didn't
update these comments.
> > +#define clocksource_adjustcheck(sign, error, interval, offset) ({ \
> > + int adj = sign; \
> > + error >>= 2; \
> > + if (unlikely(sign > 0 ? error > interval : error < interval)) { \
> > + adj = clocksource_bigadjust(sign, error, \
> > + interval, offset); \
> > + interval <<= adj; \
> > + offset <<= adj; \
> > + adj = sign << adj; \
> > + } \
> > + adj; \
> > +})
>
> That's still a #define with side effects. Yuck.
The alternative is duplicating the code and an inline function which takes
the address of these variables would likely generate worse code.
> > + clock->mult += adj;
> > + clock->xtime_interval += interval;
> > + clock->xtime_nsec -= offset;
> > + clock->error -= (interval - offset) << (TICK_LENGTH_SHIFT - clock->shift);
> > +done:
> > + /* store full nanoseconds into xtime */
> > + xtime.tv_nsec = clock->xtime_nsec >> clock->shift;
> > +}
>
> Why are you setting xtime.tv_nsec in clocksource_adjust()?
> That should be kept in update_wall_time.
clock->xtime_nsec and xtime.tv_nsec are closely related, in the long term
xtime.tv_nsec should be unused.
> > - now = clocksource_read(clock);
> > - offset = (now - last_clock_cycle)&clock->mask;
> > +#ifdef CONFIG_GENERIC_TIME
> > + offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
> > +#else
> > + offset = clock->cycle_interval;
> > +#endif
>
> This looks ok, but I'd prefer the GENERIC_TIME case to be less dense
> (not doing the read in the same line).
The "now" definition would then require another #ifdef to avoid a warning.
> > /* normally this loop will run just once, however in the
> > * case of lost or late ticks, it will accumulate correctly.
> > */
> > - while (offset > clock->interval_cycles) {
> > - /* get the ntp interval in clock shifted nanoseconds */
> > - s64 ntp_snsecs = current_tick_length(clock->shift);
> > -
> > + while (offset > clock->cycle_interval) {
>
> Shouldn't that be >= ? That was one of the fixes I made in my other
> patch.
Sorry, I indeed missed this, I was only looking at my patches.
> > /* check to see if there is a new clocksource to use */
> > if (change_clocksource()) {
> > - error = 0;
> > - remainder_snsecs = 0;
> > + clock->error = 0;
> > + clock->xtime_nsec = 0;
> > + xtime.tv_nsec = 0;
> > clocksource_calculate_interval(clock, tick_nsec);
> > }
>
> Setting xtime.tv_nsec to zero in the above is incorrect and causes the
> inconsistencies I mentioned at the top.
Indeed, but luckily it's not a common event.
bye, Roman
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