From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A353C43603 for ; Wed, 11 Dec 2019 16:44:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EF92F24653 for ; Wed, 11 Dec 2019 16:44:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730717AbfLKQos (ORCPT ); Wed, 11 Dec 2019 11:44:48 -0500 Received: from foss.arm.com ([217.140.110.172]:38696 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730621AbfLKQom (ORCPT ); Wed, 11 Dec 2019 11:44:42 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EF3601007; Wed, 11 Dec 2019 08:44:41 -0800 (PST) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 15B993F52E; Wed, 11 Dec 2019 08:44:40 -0800 (PST) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com Subject: [RFC PATCH 7/7] sched/topology: Define and use shortcut pointers for wakeup sd_flag scan Date: Wed, 11 Dec 2019 16:44:01 +0000 Message-Id: <20191211164401.5013-8-valentin.schneider@arm.com> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191211164401.5013-1-valentin.schneider@arm.com> References: <20191211164401.5013-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Reworking select_task_rq_fair()'s domain walk exposed that !want_affine wakeups only look for highest sched_domain with the required sd_flag set. This is something we can cache at sched domain build time to slightly optimize select_task_rq_fair(). Note that this isn't a "free" optimization: it costs us 3 pointers per CPU. Add cached per-CPU pointers for the highest domains with SD_BALANCE_WAKE, SD_BALANCE_EXEC and SD_BALANCE_FORK. Do note that these are exclusively used in select_task_rq_fair(), which also requires SD_LOAD_BALANCE, so the cached pointers are also gated by SD_LOAD_BALANCE (which is somewhat icky). There is another nasty thing that comes out of this: with the sched_domain/* sysctl knobs, one could e.g. clear SD_LOAD_BALANCE for some CPU(s) (AFAIK the only way to clear that flag ATM). Before this patch, that would disable entering find_idlest_cpu() from said CPU(s). With this patch, writing to the SD flags sysctl wouldn't lead to any cached SD pointer update, so we'd keep going through the slow-path. This isn't a new problem (all cached domain pointers are affected by this), but it is a change in behaviour. It could make sense to either turn this interface read-only, or add a callback in the flags update to properly update our cached domain data. Signed-off-by: Valentin Schneider --- kernel/sched/fair.c | 25 +++++++++++++------------ kernel/sched/sched.h | 3 +++ kernel/sched/topology.c | 12 ++++++++++++ 3 files changed, 28 insertions(+), 12 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ea875c7c82d7..5b72597d6540 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6344,17 +6344,6 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) int want_affine = 0; int sd_flag; - switch (wake_flags & (WF_TTWU | WF_FORK | WF_EXEC)) { - case WF_TTWU: - sd_flag = SD_BALANCE_WAKE; - break; - case WF_FORK: - sd_flag = SD_BALANCE_FORK; - break; - default: - sd_flag = SD_BALANCE_EXEC; - } - if (wake_flags & WF_TTWU) { record_wakee(p); @@ -6371,7 +6360,19 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) rcu_read_lock(); - sd = highest_flags_domain(cpu, sd_flag | SD_LOAD_BALANCE); + switch (wake_flags & (WF_TTWU | WF_FORK | WF_EXEC)) { + case WF_TTWU: + sd_flag = SD_BALANCE_WAKE; + sd = rcu_dereference(per_cpu(sd_balance_wake, cpu)); + break; + case WF_FORK: + sd_flag = SD_BALANCE_FORK; + sd = rcu_dereference(per_cpu(sd_balance_fork, cpu)); + break; + default: + sd_flag = SD_BALANCE_EXEC; + sd = rcu_dereference(per_cpu(sd_balance_exec, cpu)); + } /* * If !want_affine, we just look for the highest domain where diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 233b3d41e347..ba9d55085c7b 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1386,6 +1386,9 @@ DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc); DECLARE_PER_CPU(int, sd_llc_size); DECLARE_PER_CPU(int, sd_llc_id); DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared); +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_balance_wake); +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_balance_exec); +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_balance_fork); DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa); DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing); DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity); diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index f0d2a15fd10b..f76f40b64279 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -619,6 +619,9 @@ DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc); DEFINE_PER_CPU(int, sd_llc_size); DEFINE_PER_CPU(int, sd_llc_id); DEFINE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared); +DEFINE_PER_CPU(struct sched_domain __rcu *, sd_balance_wake); +DEFINE_PER_CPU(struct sched_domain __rcu *, sd_balance_exec); +DEFINE_PER_CPU(struct sched_domain __rcu *, sd_balance_fork); DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa); DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing); DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity); @@ -643,6 +646,15 @@ static void update_top_cache_domain(int cpu) per_cpu(sd_llc_id, cpu) = id; rcu_assign_pointer(per_cpu(sd_llc_shared, cpu), sds); + sd = highest_flags_domain(cpu, SD_BALANCE_WAKE | SD_LOAD_BALANCE); + rcu_assign_pointer(per_cpu(sd_balance_wake, cpu), sd); + + sd = highest_flags_domain(cpu, SD_BALANCE_FORK | SD_LOAD_BALANCE); + rcu_assign_pointer(per_cpu(sd_balance_fork, cpu), sd); + + sd = highest_flags_domain(cpu, SD_BALANCE_EXEC | SD_LOAD_BALANCE); + rcu_assign_pointer(per_cpu(sd_balance_exec, cpu), sd); + sd = lowest_flags_domain(cpu, SD_NUMA); rcu_assign_pointer(per_cpu(sd_numa, cpu), sd); -- 2.24.0