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SubjectRe: [PATCH 21/23] y2038: itimer: change implementation to timespec64
On Wed, 13 Nov 2019, Steven Rostedt wrote:
> On Wed, 13 Nov 2019 23:28:47 +0100 (CET)
> Thomas Gleixner <tglx@linutronix.de> wrote:
>
> > On Fri, 8 Nov 2019, Arnd Bergmann wrote:
> > > TRACE_EVENT(itimer_state,
> > >
> > > - TP_PROTO(int which, const struct itimerval *const value,
> > > + TP_PROTO(int which, const struct itimerspec64 *const value,
> > > unsigned long long expires),
> > >
> > > TP_ARGS(which, value, expires),
> > > @@ -321,12 +321,12 @@ TRACE_EVENT(itimer_state,
> > > __entry->which = which;
> > > __entry->expires = expires;
> > > __entry->value_sec = value->it_value.tv_sec;
> > > - __entry->value_usec = value->it_value.tv_usec;
> > > + __entry->value_usec = value->it_value.tv_nsec / NSEC_PER_USEC;
> > > __entry->interval_sec = value->it_interval.tv_sec;
> > > - __entry->interval_usec = value->it_interval.tv_usec;
> > > + __entry->interval_usec = value->it_interval.tv_nsec / NSEC_PER_USEC;
> >
> > Hmm, having a division in a tracepoint is clearly suboptimal.
>
> Right, we should move the division into the TP_printk()
>
> __entry->interval_nsec = alue->it_interval.tv_nsec;
>
> >
> > > ),
> > >
> > > - TP_printk("which=%d expires=%llu it_value=%ld.%ld it_interval=%ld.%ld",
> > > + TP_printk("which=%d expires=%llu it_value=%ld.%06ld it_interval=%ld.%06ld",
> >
> > We print only 6 digits after the . so that would be even correct w/o a
> > division. But it probably does not matter much.
>
> Well, we still need the division in the printk, otherwise it will print
> more than 6. That's just the minimum and it will print the full number.

That's fine. The print is not really timing critical, the tracepoint very
much so.

Thanks,

tglx

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