Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753896AbcKPTpR (ORCPT ); Wed, 16 Nov 2016 14:45:17 -0500 Received: from mail-yw0-f174.google.com ([209.85.161.174]:36222 "EHLO mail-yw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752275AbcKPTpP (ORCPT ); Wed, 16 Nov 2016 14:45:15 -0500 MIME-Version: 1.0 In-Reply-To: References: <1479315472-5245-1-git-send-email-cmetcalf@mellanox.com> From: John Stultz Date: Wed, 16 Nov 2016 11:45:13 -0800 Message-ID: Subject: Re: [PATCH] clocksource_cyc2ns: avoid overflowing 64 bits To: Chris Metcalf Cc: Thomas Gleixner , Salman Qazi , Paul Turner , Tony Lindgren , Steven Miao , lkml Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 938 Lines: 23 On Wed, Nov 16, 2016 at 11:30 AM, Chris Metcalf wrote: > diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h > index 08398182f56e..5444429884b8 100644 > --- a/include/linux/clocksource.h > +++ b/include/linux/clocksource.h > @@ -171,6 +171,10 @@ static inline u32 clocksource_hz2mult(u32 hz, u32 > shift_constant) > * > * Converts cycles to nanoseconds, using the given mult and shift. > * > + * The code is optimized for performance and not intended to work > + * with absolute clocksource cycles, as it will easily overflow, > + * but just intended for relative (delta) clocksource cycles. > + * > * XXX - This could use some mult_lxl_ll() asm optimization Just as a heads up, it seems your working against an older kernel, as this didn't apply. Its simple enough to fix up, so I'll do so, but in the future, please submit patches against something close to Linus HEAD. thanks -john