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Date: Sat, 17 Mar 2012 15:06:54 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Felix Fietkau <nbd@...nwrt.org> Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de Subject: Re: [PATCH] timer: optimize apply_slack() On Sat, 2012-03-17 at 22:31 +0100, Felix Fietkau wrote: > __fls(mask) is equivalent to find_last_bit(&mask, BITS_PER_LONG), but cheaper. > find_last_bit was showing up high on the list when I was profiling for stalls > on icache misses on a system with very small cache size (MIPS). > > Signed-off-by: Felix Fietkau <nbd@...nwrt.org> > --- > kernel/timer.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/timer.c b/kernel/timer.c > index a297ffc..659371e 100644 > --- a/kernel/timer.c > +++ b/kernel/timer.c > @@ -809,7 +809,7 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires) > if (mask == 0) > return expires; > > - bit = find_last_bit(&mask, BITS_PER_LONG); > + bit = __fls(mask); > > mask = (1 << bit) - 1; > Not a comment on your patch, but this code seems not correct. This probably should be : mask = (1UL << bit) - 1; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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