Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754872AbbB0PzQ (ORCPT ); Fri, 27 Feb 2015 10:55:16 -0500 Received: from mail-wg0-f53.google.com ([74.125.82.53]:33539 "EHLO mail-wg0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751693AbbB0PzN (ORCPT ); Fri, 27 Feb 2015 10:55:13 -0500 From: Vincent Guittot To: peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org, preeti@linux.vnet.ibm.com, Morten.Rasmussen@arm.com, kamalesh@linux.vnet.ibm.com Cc: riel@redhat.com, efault@gmx.de, nicolas.pitre@linaro.org, dietmar.eggemann@arm.com, linaro-kernel@lists.linaro.org, Vincent Guittot Subject: [PATCH v10 05/11] sched: make scale_rt invariant with frequency Date: Fri, 27 Feb 2015 16:54:08 +0100 Message-Id: <1425052454-25797-6-git-send-email-vincent.guittot@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1425052454-25797-1-git-send-email-vincent.guittot@linaro.org> References: <1425052454-25797-1-git-send-email-vincent.guittot@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3562 Lines: 103 The average running time of RT tasks is used to estimate the remaining compute capacity for CFS tasks. This remaining capacity is the original capacity scaled down by a factor (aka scale_rt_capacity). This estimation of available capacity must also be invariant with frequency scaling. A frequency scaling factor is applied on the running time of the RT tasks for computing scale_rt_capacity. In sched_rt_avg_update, we now scale the RT execution time like below: rq->rt_avg += rt_delta * arch_scale_freq_capacity() >> SCHED_CAPACITY_SHIFT Then, scale_rt_capacity can be summarized by: scale_rt_capacity = SCHED_CAPACITY_SCALE * available / total with available = total - rq->rt_avg This has been been optimized in current code by scale_rt_capacity = available / (total >> SCHED_CAPACITY_SHIFT) But we can also developed the equation like below scale_rt_capacity = SCHED_CAPACITY_SCALE - ((rq->rt_avg << SCHED_CAPACITY_SHIFT) / total) and we can optimize the equation by removing SCHED_CAPACITY_SHIFT shift in the computation of rq->rt_avg and scale_rt_capacity so rq->rt_avg += rt_delta * arch_scale_freq_capacity() and scale_rt_capacity = SCHED_CAPACITY_SCALE - (rq->rt_avg / total) arch_scale_frequency_capacity will be called in the hot path of the scheduler which implies to have a short and efficient function. As an example, arch_scale_frequency_capacity should return a cached value that is updated periodically outside of the hot path. Signed-off-by: Vincent Guittot Acked-by: Morten Rasmussen --- kernel/sched/fair.c | 17 +++++------------ kernel/sched/sched.h | 4 +++- 2 files changed, 8 insertions(+), 13 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7f031e4..dc7c693 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6004,7 +6004,7 @@ unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu) static unsigned long scale_rt_capacity(int cpu) { struct rq *rq = cpu_rq(cpu); - u64 total, available, age_stamp, avg; + u64 total, used, age_stamp, avg; s64 delta; /* @@ -6020,19 +6020,12 @@ static unsigned long scale_rt_capacity(int cpu) total = sched_avg_period() + delta; - if (unlikely(total < avg)) { - /* Ensures that capacity won't end up being negative */ - available = 0; - } else { - available = total - avg; - } + used = div_u64(avg, total); - if (unlikely((s64)total < SCHED_CAPACITY_SCALE)) - total = SCHED_CAPACITY_SCALE; + if (likely(used < SCHED_CAPACITY_SCALE)) + return SCHED_CAPACITY_SCALE - used; - total >>= SCHED_CAPACITY_SHIFT; - - return div_u64(available, total); + return 1; } static void update_cpu_capacity(struct sched_domain *sd, int cpu) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 65fa7b5..23c6dd7 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1374,9 +1374,11 @@ static inline int hrtick_enabled(struct rq *rq) #ifdef CONFIG_SMP extern void sched_avg_update(struct rq *rq); +extern unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu); + static inline void sched_rt_avg_update(struct rq *rq, u64 rt_delta) { - rq->rt_avg += rt_delta; + rq->rt_avg += rt_delta * arch_scale_freq_capacity(NULL, cpu_of(rq)); sched_avg_update(rq); } #else -- 1.9.1 -- 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/