Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 22 Jun 2018 09:22:22 +0100
From:   Quentin Perret <quentin.perret@arm.com>
To:     Morten Rasmussen <morten.rasmussen@arm.com>
Cc:     peterz@infradead.org, mingo@redhat.com, valentin.schneider@arm.com,
        dietmar.eggemann@arm.com, vincent.guittot@linaro.org,
        gaku.inami.xh@renesas.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv3 1/9] sched: Add static_key for asymmetric cpu capacity
 optimizations
Message-ID: <20180622082222.GD23168@e108498-lin.cambridge.arm.com>
References: <1529485549-5191-1-git-send-email-morten.rasmussen@arm.com>
 <1529485549-5191-2-git-send-email-morten.rasmussen@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1529485549-5191-2-git-send-email-morten.rasmussen@arm.com>
User-Agent: Mutt/1.8.3 (2017-05-23)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Morten,

On Wednesday 20 Jun 2018 at 10:05:41 (+0100), Morten Rasmussen wrote:
> +static void update_asym_cpucapacity(int cpu)
> +{
> +	int enable = false;
> +
> +	rcu_read_lock();
> +	if (lowest_flag_domain(cpu, SD_ASYM_CPUCAPACITY))
> +		enable = true;
> +	rcu_read_unlock();
> +
> +	if (enable) {
> +		/* This expects to be hotplug-safe */
> +		static_branch_enable_cpuslocked(&sched_asym_cpucapacity);
> +	}
> +}

What would happen if you hotplugged an entire cluster ? You'd loose the
SD_ASYM_CPUCAPACITY flag but keep the static key is that right ? Should
we care ?

And also, Peter mentioned an issue with the EAS patches with multiple
root_domains. Does that apply here as well ? What if you had a
configuration with big and little CPUs in different root_domains for ex?

Should we disable the static key in the above cases ?

Thanks,
Quentin