Messages in this thread | | | Date | Thu, 28 Feb 2008 22:58:49 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] Prevent the loop in timespec_add_ns() to be optimised away |
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On Wed, 27 Feb 2008, Andrew Morton wrote:
> On Fri, 22 Feb 2008 22:40:45 +0100 > Segher Boessenkool <segher@kernel.crashing.org> wrote: > > > ...since some architectures don't support __udivdi3() (and > > we don't want to use that, anyway). > > > > Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org> > > --- > > include/linux/time.h | 4 ++++ > > 1 files changed, 4 insertions(+), 0 deletions(-) > > > > diff --git a/include/linux/time.h b/include/linux/time.h > > index 2091a19..d32ef0a 100644 > > --- a/include/linux/time.h > > +++ b/include/linux/time.h > > @@ -174,6 +174,10 @@ static inline void timespec_add_ns(struct timespec *a, u64 ns) > > { > > ns += a->tv_nsec; > > while(unlikely(ns >= NSEC_PER_SEC)) { > > + /* The following asm() prevents the compiler from > > + * optimising this loop into a modulo operation. */ > > + asm("" : "+r"(ns)); > > + > > ns -= NSEC_PER_SEC; > > a->tv_sec++; > > } > > It's pretty sad that we need to turn this into a loop just because of the > __udivdi3() thing. > > otoh, it's rarely occurring, and it could be that the number of times it > loops is usually 1 (if it wasn't zero), so perhaps a loop is faster than a > divide anyway. > > This code is probably too large to be inlined. > > I queued this patch as needed-in-2.6.25, to-be-merged-via-Thomas.
Are you going to send it or should I grab it from the mailing list myself ?
Thanks, tglx
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