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Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1g805q-0001rG-Nu; Thu, 04 Oct 2018 09:38:51 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 45E52202695A2; Thu, 4 Oct 2018 11:38:48 +0200 (CEST) Date: Thu, 4 Oct 2018 11:38:48 +0200 From: Peter Zijlstra To: Quentin Perret Cc: rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, gregkh@linuxfoundation.org, mingo@redhat.com, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, patrick.bellasi@arm.com, valentin.schneider@arm.com, vincent.guittot@linaro.org, thara.gopinath@linaro.org, viresh.kumar@linaro.org, tkjos@google.com, joel@joelfernandes.org, smuckle@google.com, adharmap@codeaurora.org, skannan@codeaurora.org, pkondeti@codeaurora.org, juri.lelli@redhat.com, edubezval@gmail.com, srinivas.pandruvada@linux.intel.com, currojerez@riseup.net, javi.merino@kernel.org Subject: Re: [PATCH v7 08/14] sched/topology: Disable EAS on inappropriate platforms Message-ID: <20181004093848.GM19272@hirez.programming.kicks-ass.net> References: <20180912091309.7551-1-quentin.perret@arm.com> <20180912091309.7551-9-quentin.perret@arm.com> <20181003162719.GB19252@hirez.programming.kicks-ass.net> <20181004091046.7nn2odqrjy7tp5vx@queper01-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181004091046.7nn2odqrjy7tp5vx@queper01-lin> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 04, 2018 at 10:10:48AM +0100, Quentin Perret wrote: > On Wednesday 03 Oct 2018 at 18:27:19 (+0200), Peter Zijlstra wrote: > > On Wed, Sep 12, 2018 at 10:13:03AM +0100, Quentin Perret wrote: > > > @@ -288,6 +321,21 @@ static void build_perf_domains(const struct cpumask *cpu_map) > > > goto free; > > > tmp->next = pd; > > > pd = tmp; > > > + > > > + /* > > > + * Count performance domains and capacity states for the > > > + * complexity check. > > > + */ > > > + nr_pd++; > > > + nr_cs += em_pd_nr_cap_states(pd->obj); > > > + } > > > + > > > + /* Bail out if the Energy Model complexity is too high. */ > > > + if (nr_pd * (nr_cs + nr_cpus) > EM_MAX_COMPLEXITY) { > > > + if (sched_debug()) > > > + pr_info("rd %*pbl: EM complexity is too high\n ", > > > + cpumask_pr_args(cpu_map)); > > > + goto free; > > > } > > > > I would make than an unconditional WARN, we do not really expect that to > > trigger, but then it does, we really don't want to hide it. > > OTOH that also means that some people with big asymmetric machines can > get a WARN message every time they boot, and even if they don't want to > use EAS. > > Now, that shouldn't happen any time soon, so it's maybe a good thing if > we get reports when/if people start to hit that one, so why not ... Right, and if becomes a real problem we can think of a solution (like maybe a DT thingy that says to not use EAS, or a 'better' EAS algorithm).