Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753279AbcD1KrA (ORCPT ); Thu, 28 Apr 2016 06:47:00 -0400 Received: from mga02.intel.com ([134.134.136.20]:49305 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753139AbcD1KiX (ORCPT ); Thu, 28 Apr 2016 06:38:23 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,546,1455004800"; d="scan'208";a="964534397" From: Yuyang Du To: peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org Cc: bsegall@google.com, pjt@google.com, morten.rasmussen@arm.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, juri.lelli@arm.com, Yuyang Du Subject: [PATCH 3/6] sched/fair: Change the variable to hold the number of periods to 32bit integer Date: Thu, 28 Apr 2016 10:56:10 +0800 Message-Id: <1461812173-32439-4-git-send-email-yuyang.du@intel.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1461812173-32439-1-git-send-email-yuyang.du@intel.com> References: <1461812173-32439-1-git-send-email-yuyang.du@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2690 Lines: 85 Now a period is about 1ms, so a 32-bit unsigned integer can approximately hold a maximum of 49 (=2^32/1000/3600/24) days, which means it is big enough and 64-bit is needless. Signed-off-by: Yuyang Du --- kernel/sched/fair.c | 27 +++++++++++++-------------- 1 file changed, 13 insertions(+), 14 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8d49276..abfe17a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2619,18 +2619,13 @@ static const u32 __accumulated_sum_N32[] = { * n is the number of periods past; a period is ~1ms * m is called half-life in exponential decay; here it is SCHED_AVG_HALFLIFE=32. */ -static __always_inline u64 __decay_sum(u64 val, u64 n) +static __always_inline u64 __decay_sum(u64 val, u32 n) { - unsigned int local_n; - if (!n) return val; else if (unlikely(n > SCHED_AVG_HALFLIFE * 63)) return 0; - /* after bounds checking we can collapse to 32-bit */ - local_n = n; - /* * As y^PERIOD = 1/2, we can combine * y^n = 1/2^(n/PERIOD) * y^(n%PERIOD) @@ -2638,12 +2633,12 @@ static __always_inline u64 __decay_sum(u64 val, u64 n) * * To achieve constant time decay_load. */ - if (unlikely(local_n >= SCHED_AVG_HALFLIFE)) { - val >>= local_n / SCHED_AVG_HALFLIFE; - local_n %= SCHED_AVG_HALFLIFE; + if (unlikely(n >= SCHED_AVG_HALFLIFE)) { + val >>= n / SCHED_AVG_HALFLIFE; + n %= SCHED_AVG_HALFLIFE; } - val = mul_u64_u32_shr(val, __decay_inv_multiply_N[local_n], 32); + val = mul_u64_u32_shr(val, __decay_inv_multiply_N[n], 32); return val; } @@ -2654,7 +2649,7 @@ static __always_inline u64 __decay_sum(u64 val, u64 n) * We can compute this efficiently by combining: * y^32 = 1/2 with precomputed \Sum 1024*y^n (where n < 32) */ -static u32 __accumulate_sum(u64 n) +static u32 __accumulate_sum(u32 n) { u32 contrib = 0; @@ -2708,8 +2703,8 @@ static __always_inline int __update_sched_avg(u64 now, int cpu, struct sched_avg *sa, unsigned long weight, int running, struct cfs_rq *cfs_rq) { - u64 delta, scaled_delta, periods; - u32 contrib; + u64 delta, scaled_delta; + u32 contrib, periods; unsigned int delta_w, scaled_delta_w, decayed = 0; unsigned long scale_freq, scale_cpu; @@ -2762,7 +2757,11 @@ __update_sched_avg(u64 now, int cpu, struct sched_avg *sa, delta -= delta_w; - /* Figure out how many additional periods this update spans */ + /* + * Figure out how many additional periods this update spans. + * A period is 1024*1024ns or ~1ms, so a 32bit integer can hold + * approximately a maximum of 49 (=2^32/1000/3600/24) days. + */ periods = delta / 1024; delta %= 1024; -- 1.7.9.5