Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754616Ab3CFHTJ (ORCPT ); Wed, 6 Mar 2013 02:19:09 -0500 Received: from mga11.intel.com ([192.55.52.93]:37047 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752451Ab3CFHTF (ORCPT ); Wed, 6 Mar 2013 02:19:05 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,793,1355126400"; d="scan'208";a="299868748" From: Feng Tang To: Thomas Gleixner , John Stultz , Ingo Molnar , "H. Peter Anvin" , Jason Gunthorpe , x86@kernel.org, Len Brown , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org Cc: gong.chen@linux.intel.com, Feng Tang Subject: [PATCH v3 4/5] clocksource: Enable clocksource_cyc2ns() to cover big cycles Date: Wed, 6 Mar 2013 15:17:50 +0800 Message-Id: <1362554271-22382-5-git-send-email-feng.tang@intel.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1362554271-22382-1-git-send-email-feng.tang@intel.com> References: <1362554271-22382-1-git-send-email-feng.tang@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1398 Lines: 41 Current clocksource_cyc2ns() has a implicit limit that the (cycles * mult) can not exceed 64 bits limit. Jason Gunthorpe proposed a way to handle this big cycles case, and this patch put the handling into clocksource_cyc2ns() so that it could be used unconditionally. Suggested-by: Jason Gunthorpe Signed-off-by: Feng Tang --- include/linux/clocksource.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index aa7032c..1ecc872 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -274,7 +274,16 @@ static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant) */ static inline s64 clocksource_cyc2ns(cycle_t cycles, u32 mult, u32 shift) { - return ((u64) cycles * mult) >> shift; + u64 max = ULLONG_MAX / mult; + s64 nsec = 0; + + /* The (mult * cycles) may overflow 64 bits, so add a max check */ + if (cycles > max) { + nsec = ((max * mult) >> shift) * (cycles / max); + cycles %= max; + } + nsec += ((u64) cycles * mult) >> shift; + return nsec; } -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/