From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161041Ab2CQWHO (ORCPT ); Sat, 17 Mar 2012 18:07:14 -0400 Received: from mail-pz0-f46.google.com ([209.85.210.46]:37745 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030235Ab2CQWG6 (ORCPT ); Sat, 17 Mar 2012 18:06:58 -0400 Subject: Re: [PATCH] timer: optimize apply_slack() From: Eric Dumazet To: Felix Fietkau Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de In-Reply-To: <1332019895-59698-1-git-send-email-nbd@openwrt.org> References: <1332019895-59698-1-git-send-email-nbd@openwrt.org> Content-Type: text/plain; charset="UTF-8" Date: Sat, 17 Mar 2012 15:06:54 -0700 Message-ID: <1332022014.9397.2.camel@edumazet-glaptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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;