* Roman Zippel <[email protected]> wrote:
> > This adds an artificial offset to the expiry time, for what reason? The
> > expiry code makes sure that timers can not expire early. See:
> >
> > timer = rb_entry(node, struct hrtimer, node);
> > if (now.tv64 <= timer->expires.tv64)
> > break;
> >
> > in kernel/hrtimers.c:run_hrtimer_queue(), where now is already tick
> > aligned.
> >
> > Please provide a testcase (or detailed use-case) which proves that this
> > is necessary.
>
> Let's assume a get_time() which simply returns xtime and so has a
> resolution of around TICK_NSEC. This means the real time when one
> calls get_time() is somewhere between xtime and xtime+TICK_NSEC.
> Assuming the real time is xtime+TICK_NSEC-1, get_time() will return
> xtime and a relative timer with TICK_NSEC-1 will expire immediately.
> The old code did this correctly. For most hardware this is not a real
> issue, as the delivery time is larger than the clock resolution, but
> unless you can guarantee it's not an issue on _any_ supported
> hardware, this fix is needed. As I already said this can be better
> fixed as soon as we have a better clock abstraction, until then this
> is only restores the old behaviour.
but there is no 'old behavior' to restore to. The +1 to itimer intervals
caused artifacts that were hitting users and caused 2.4 -> 2.6 itimer
regressions, which hrtimers fixed. E.g.:
http://bugzilla.kernel.org/show_bug.cgi?id=3289
so i dont think restoring the first timeout of an interval timer to be
increased by resolution [which your patch does] has any meaning. It
'restores' to half of what 2.6 did prior hrtimers. Doing that would be
inconsistent and would push the 'sum-up' errors observed for interval
timers above to be again observable in user-space (if user-space does a
series of timeouts). What's the point?
Ingo
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