From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature Date: Wed, 26 Oct 2016 13:24:27 +0200 (CEST) Message-ID: References: <20161026112502.GB3117@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <20161026112502.GB3117@twins.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: Tim Chen , rjw@rjwysocki.net, mingo@redhat.com, bp@suse.de, x86@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, jolsa@redhat.com, Srinivas Pandruvada List-Id: linux-pm@vger.kernel.org On Wed, 26 Oct 2016, Peter Zijlstra wrote: > On Wed, Oct 26, 2016 at 12:49:36PM +0200, Thomas Gleixner wrote: > > > > + /* > > > + * ITMT capability automatically enables ITMT > > > + * scheduling for small systems (single node). > > > + */ > > > + if (topology_num_packages() == 1) > > > + sysctl_sched_itmt_enabled = 1; > > > > I really hate this. This is policy and the kernel should not impose > > policy. Why would I like to have this enforced on my single socket XEON > > server? > > So this really wants to be enabled by default; otherwise nobody will use > this, and it really does help single threaded workloads. Fair enough. Then this wants to be documented. > There were reservations on the multi-socket case of ITMT, maybe it would > help to spell those out in great detail here. That is, have the comment > explain the policy instead of simply stating what the code does (which > is always bad comment policy, you can read the code just fine). What is the objection for multi sockets? If it improves the behaviour then why would this be a bad thing for multi sockets? Thanks, tglx