From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 04/11] sched,x86: Enable Turbo Boost Max Technology Date: Wed, 24 Aug 2016 12:18:53 +0200 Message-ID: <20160824101853.GA25705@gmail.com> References: <1471559812-19967-1-git-send-email-srinivas.pandruvada@linux.intel.com> <1471559812-19967-5-git-send-email-srinivas.pandruvada@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1471559812-19967-5-git-send-email-srinivas.pandruvada@linux.intel.com> Sender: linux-acpi-owner@vger.kernel.org To: Srinivas Pandruvada Cc: mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, rjw@rjwysocki.net, peterz@infradead.org, x86@kernel.org, bp@suse.de, sudeep.holla@arm.com, ak@linux.intel.com, linux-acpi@vger.kernel.org, linux-pm@vger.kernel.org, alexey.klimov@arm.com, viresh.kumar@linaro.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, lenb@kernel.org, tim.c.chen@linux.intel.com, paul.gortmaker@windriver.com, jpoimboe@redhat.com, mcgrof@kernel.org, jgross@suse.com, robert.moore@intel.com, dvyukov@google.com, jeyu@redhat.com, Peter Zijlstra List-Id: linux-pm@vger.kernel.org * Srinivas Pandruvada wrote: > From: Tim Chen > > On some Intel cores, they can boosted to a higher turbo frequency than > the other cores on the same die. So we prefer processes to be run on > them vs other lower frequency ones for extra performance. > > We extend the asym packing feature in the scheduler to support packing > task to the higher frequency core at the core sched domain level. > > We set up a core priority metric to abstract the core preferences based > on the maximum boost frequency. The priority is instantiated such that > the core with a higher priority is favored over the core with lower > priority when making scheduling decision using ASYM_PACKING. The smt > threads that are of higher number are discounted in their priority so > we will not try to pack tasks onto all the threads of a favored core > before using other cpu cores. The cpu that's of the highese priority > in a sched_group is recorded in sched_group->asym_prefer_cpu during > initialization to save lookup during load balancing. > > A sysctl variable /proc/sys/kernel/sched_itmt_enabled is provided so > the scheduling based on favored core can be turned on or off at run time. > +/* > + * Boolean to control whether we want to move processes to cpu capable > + * of higher turbo frequency for cpus supporting Intel Turbo Boost Max > + * Technology 3.0. > + * > + * It can be set via /proc/sys/kernel/sched_itmt_enabled > + */ > +unsigned int __read_mostly sysctl_sched_itmt_enabled = 0; Ugh, no. We don't add features to the scheduler in the hope that they might or might not help. We either enable a new feature by default (and make damn sure it helps!), or don't add the feature at all. Thanks, Ingo