From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756457AbbFQXVx (ORCPT ); Wed, 17 Jun 2015 19:21:53 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35107 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932794AbbFQW0H (ORCPT ); Wed, 17 Jun 2015 18:26:07 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Arnd Bergmann , Thomas Gleixner , Ingo Molnar , Nicolas Pitre , John Stultz , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 095/146] ktime: Optimize ktime_divns for constant divisors Date: Wed, 17 Jun 2015 15:23:20 -0700 Message-Id: <1434579851-1719-96-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1434579851-1719-1-git-send-email-kamal@canonical.com> References: <1434579851-1719-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.19.8-ckt2 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Nicolas Pitre commit 8b618628b2bf83512fc8df5e8672619d65adfdfb upstream. At least on ARM, do_div() is optimized to turn constant divisors into an inline multiplication by the reciprocal value at compile time. However this optimization is missed entirely whenever ktime_divns() is used and the slow out-of-line division code is used all the time. Let ktime_divns() use do_div() inline whenever the divisor is constant and small enough. This will make things like ktime_to_us() and ktime_to_ms() much faster. Cc: Arnd Bergmann Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Nicolas Pitre Acked-by: Arnd Bergmann Signed-off-by: Nicolas Pitre Signed-off-by: John Stultz Signed-off-by: Kamal Mostafa --- include/linux/ktime.h | 12 +++++++++++- kernel/time/hrtimer.c | 4 ++-- 2 files changed, 13 insertions(+), 3 deletions(-) diff --git a/include/linux/ktime.h b/include/linux/ktime.h index c9d645a..411dd8b 100644 --- a/include/linux/ktime.h +++ b/include/linux/ktime.h @@ -166,7 +166,17 @@ static inline bool ktime_before(const ktime_t cmp1, const ktime_t cmp2) } #if BITS_PER_LONG < 64 -extern u64 ktime_divns(const ktime_t kt, s64 div); +extern u64 __ktime_divns(const ktime_t kt, s64 div); +static inline u64 ktime_divns(const ktime_t kt, s64 div) +{ + if (__builtin_constant_p(div) && !(div >> 32)) { + u64 ns = kt.tv64; + do_div(ns, div); + return ns; + } else { + return __ktime_divns(kt, div); + } +} #else /* BITS_PER_LONG < 64 */ # define ktime_divns(kt, div) (u64)((kt).tv64 / (div)) #endif diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index d8c724c..5e4d51c 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -266,7 +266,7 @@ lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags) /* * Divide a ktime value by a nanosecond value */ -u64 ktime_divns(const ktime_t kt, s64 div) +u64 __ktime_divns(const ktime_t kt, s64 div) { u64 dclc; int sft = 0; @@ -282,7 +282,7 @@ u64 ktime_divns(const ktime_t kt, s64 div) return dclc; } -EXPORT_SYMBOL_GPL(ktime_divns); +EXPORT_SYMBOL_GPL(__ktime_divns); #endif /* BITS_PER_LONG >= 64 */ /* -- 1.9.1