From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AIpwx499V6xp4MAoJEbg4pig/krtMLXp3Cyn+F0uqCU2zHSKJQTure8T8thpBwa8+KowbkJFWO3d ARC-Seal: i=1; a=rsa-sha256; t=1523267585; cv=none; d=google.com; s=arc-20160816; b=cjKWwX9Xliisygux4PdeCsodJIP2Utct78mKw5ngPlAw4GANFm46U2M3LDiF595L22 BbIMbkA6M3NzWUMUUNWMfxWfFFyLKMp7tuWBVONslIrnl2h/EMbchmFc/PhFJoJWU1QE c0vMQTm5O0l6byn6gD7skV7jKX3CwyKQM0ZYGiEyq6aM31tN6PPtuRLVc1BzetSDLgjV jh8mrOJWtFGf0MzZ/f1cVDzxuE2dVGS5y2Aa0wa7Jf7w/5E4hFFX2lA0H86GJ+jp+2El U7G8qT4LbGmWhgxtAuBNiov3VeDSTdWlT97BdbQ19QG3J1KgvfdzC6Uwr7e3VsF5zflT HfEg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject :arc-authentication-results; bh=4D+RgcpfZhKSmvhObqOJE3FBxhHjFtqoiffkI7QWk2k=; b=1BZnZxvoRugBkXm7M9Xhcb6sNm/sf2JSMFQljB/Behu5Eb26RNvtyeerUWKOc1yP7w sfY8TM/vA+9Lgk4/wPvYW3Q0T1d4pY1WFQkjdk5HdtHquYQZzPKPamvHEwRjvYB5gg7V nKcmwGxq1vc3mQi7v6UMavSbJMhJFRdfJYvzgaRt4bPXd0wUYHxvoy9iAFGw+7Tf2YQq 7y9Mc2BM+hEV9AnciMKSTVdk/x6mq7DI5DNt5hv5QkMWDkHzw9J+MVm4zGBvK3hrE6Mt 5GZBEPUK7gRzPfrlX/FoNpgxpRY9yTuIDRDw/BGdU/+EoZ+heGlMQyelBwcJEF6Q8xm+ tNJA== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of dietmar.eggemann@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=dietmar.eggemann@arm.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of dietmar.eggemann@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=dietmar.eggemann@arm.com Subject: Re: [RFC PATCH 3/6] sched: Add over-utilization/tipping point indicator To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Quentin Perret , Thara Gopinath , linux-pm@vger.kernel.org, Morten Rasmussen , Chris Redpath , Patrick Bellasi , Valentin Schneider , "Rafael J . Wysocki" , Greg Kroah-Hartman , Vincent Guittot , Viresh Kumar , Todd Kjos , Joel Fernandes References: <20180320094312.24081-1-dietmar.eggemann@arm.com> <20180320094312.24081-4-dietmar.eggemann@arm.com> <20180409094001.GZ4043@hirez.programming.kicks-ass.net> From: Dietmar Eggemann Message-ID: <093ba425-4f81-9f86-78a6-1cd1fd4651f9@arm.com> Date: Mon, 9 Apr 2018 11:53:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <20180409094001.GZ4043@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1595449336588138126?= X-GMAIL-MSGID: =?utf-8?q?1597261832190079903?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 04/09/2018 11:40 AM, Peter Zijlstra wrote: > > (I know there is a new version out; but I was reading through this to > catch up with the discussion) > > On Tue, Mar 20, 2018 at 09:43:09AM +0000, Dietmar Eggemann wrote: >> +static inline int sd_overutilized(struct sched_domain *sd) >> +{ >> + return READ_ONCE(sd->shared->overutilized); >> +} >> + >> +static inline void update_overutilized_status(struct rq *rq) >> +{ >> + struct sched_domain *sd; >> + >> + rcu_read_lock(); >> + sd = rcu_dereference(rq->sd); >> + if (sd && !sd_overutilized(sd) && cpu_overutilized(rq->cpu)) >> + WRITE_ONCE(sd->shared->overutilized, 1); >> + rcu_read_unlock(); >> +} >> +#else > > I think you ought to go have a look at the end of > kernel/sched/topology.c:sd_init(), where it says: > > /* > * For all levels sharing cache; connect a sched_domain_shared > * instance. > */ > if (sd->flags & SD_SHARE_PKG_RESOURCES) { > sd->shared = *per_cpu_ptr(sdd->sds, sd_id); > atomic_inc(&sd->shared->ref); > atomic_set(&sd->shared->nr_busy_cpus, sd_weight); > } > > Because if I read all this correctly, your code assumes sd->shared > exists unconditionally, while the quoted bit only ensures it does so <= > LLC. > But the patch changes this part further down. diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 64cc564f5255..c8b7c7665ab2 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1184,15 +1184,11 @@ sd_init(struct sched_domain_topology_level *tl, sd->idle_idx = 1; } - /* - * For all levels sharing cache; connect a sched_domain_shared - * instance. - */ - if (sd->flags & SD_SHARE_PKG_RESOURCES) { - sd->shared = *per_cpu_ptr(sdd->sds, sd_id); - atomic_inc(&sd->shared->ref); + sd->shared = *per_cpu_ptr(sdd->sds, sd_id); + atomic_inc(&sd->shared->ref); + + if (sd->flags & SD_SHARE_PKG_RESOURCES) atomic_set(&sd->shared->nr_busy_cpus, sd_weight); - }