On Mon, Dec 01, 2014 at 01:24:52PM +0100, Heiko Carstens wrote: > On Fri, Nov 28, 2014 at 07:23:36PM +0100, Frederic Weisbecker wrote: > > This will be needed for the conversion of kernel stat to nsecs. > > > > Cc: Benjamin Herrenschmidt <[email protected]> > > Cc: Heiko Carstens <[email protected]> > > Cc: Ingo Molnar <[email protected]> > > Cc: Martin Schwidefsky <[email protected]> > > Cc: Oleg Nesterov <[email protected]> > > Cc: Paul Mackerras <[email protected]> > > Cc: Peter Zijlstra <[email protected]> > > Cc: Rik van Riel <[email protected]> > > Cc: Thomas Gleixner <[email protected]> > > Cc: Tony Luck <[email protected]> > > Cc: Wu Fengguang <[email protected]> > > Signed-off-by: Frederic Weisbecker <[email protected]> > > --- > > arch/s390/include/asm/cputime.h | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/arch/s390/include/asm/cputime.h > > b/arch/s390/include/asm/cputime.h > > index 820b38a..75ba96f 100644 > > --- a/arch/s390/include/asm/cputime.h > > +++ b/arch/s390/include/asm/cputime.h > > @@ -59,6 +59,11 @@ static inline cputime64_t jiffies64_to_cputime64(const > > u64 jif) > > return (__force cputime64_t)(jif * (CPUTIME_PER_SEC / HZ)); > > } > > > > +static inline u64 cputime64_to_nsecs(cputime64_t cputime) > > +{ > > + return (__force u64)cputime * CPUTIME_PER_USEC * NSEC_PER_USEC; > > +} > > + > > This is incorrect. You probably wanted to write something like > > return (__force u64)cputime / CPUTIME_PER_USEC * NSEC_PER_USEC; ?
You're right :-) > > However we would still lose a lot of precision. > The correct algorithm to convert from cputime to nanoseconds can be found in > tod_to_ns() - see arch/s390/include/asm/timex.h > > And if you see that rather complex algorithm, I doubt we want to have the > changes you propose. We need to have that calculation three times for each > irq (user, system and steal time) and would still have worse precision than > we have right now. Not talking about the additional wasted cpu cycles... Yeah indeed. So probably it could be better to accumulate the time in cputime_t and flush it as nsecs on tick. > > But I guess Martin wanted to comment on your patches anyway ;) > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
