From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756550AbaCDIFQ (ORCPT ); Tue, 4 Mar 2014 03:05:16 -0500 Received: from mail-lb0-f179.google.com ([209.85.217.179]:37919 "EHLO mail-lb0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752195AbaCDIFN (ORCPT ); Tue, 4 Mar 2014 03:05:13 -0500 Date: Tue, 4 Mar 2014 09:02:31 +0100 From: Henrik Austad To: Mike Galbraith Cc: John Stultz , Salman Qazi , LKML Subject: Re: [RFC][PATCH] clocksource: avoid unnecessary overflow in cyclecounter_cyc2ns() Message-ID: <20140304080231.GB18178@austad.us> References: <1393910409.6415.9.camel@marge.simpson.net> <20140304072020.GA18178@austad.us> <1393918280.5419.19.camel@marge.simpson.net> <1393918588.5419.23.camel@marge.simpson.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1393918588.5419.23.camel@marge.simpson.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 04, 2014 at 08:36:28AM +0100, Mike Galbraith wrote: > (boing boing boing... hell with it, today doesn't exist;) you lost me at boing.. :) > On Tue, 2014-03-04 at 08:31 +0100, Mike Galbraith wrote: > > On Tue, 2014-03-04 at 08:20 +0100, Henrik Austad wrote: > > > On Tue, Mar 04, 2014 at 06:20:09AM +0100, Mike Galbraith wrote: > > > > Greetings, > > > > > > > > While rummaging around looking for HTH a gaggle of weird a$$ machines > > > > can manage to timewarp back and forth by exactly 208 days, I stumbled > > > > across $subject which looks like it may want to borrow Salman's fix. > > > > > > > > clocksource: avoid unnecessary overflow in cyclecounter_cyc2ns() > > > > > > > > As per 4cecf6d401a "sched, x86: Avoid unnecessary overflow in sched_clock", > > > > cycles * mult >> shift is overflow prone. so give it the same treatment. > > > > > > > > Cc: Salman Qazi > > > > Cc: John Stultz > > > > Signed-off-by: Mike Galbraith > > > > --- > > > > include/linux/clocksource.h | 11 ++++++++--- > > > > 1 file changed, 8 insertions(+), 3 deletions(-) > > > > > > > > --- a/include/linux/clocksource.h > > > > +++ b/include/linux/clocksource.h > > > > @@ -77,13 +77,18 @@ struct timecounter { > > > > * > > > > * XXX - This could use some mult_lxl_ll() asm optimization. Same code > > > > * as in cyc2ns, but with unsigned result. > > > > + * > > > > + * Because it is the same as x86 __cycles_2_ns, give it the same treatment as > > > > + * commit 4cecf6d401a "sched, x86: Avoid unnecessary overflow in sched_clock" > > > > + * to avoid a potential cycles * mult overflow. > > > > > > Do we normally reference a particular commit in a comment? Why not just > > > grab the same comment and add a "this is grabbed from arch/x86/... ? > > > > Fewer '+' signs? History doesn't go away, so seems fine to me. I wasn't thinking about the number of +'s in the code, but rather referencing other parts of the code from the code and particular commits in the commit-msg itself. It was the code<->commitmsg interface I was pondering. Besides, it wasn't meant as "you shouldn't do that", but more "is it ok to do that?" :) -- Henrik Austad