From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <4F0C5138.5010109@linux.intel.com> Date: Tue, 10 Jan 2012 06:54:48 -0800 From: Arjan van de Ven MIME-Version: 1.0 To: Peter Zijlstra CC: Ingo Molnar , Suresh Siddha , Youquan Song , linux-kernel@vger.kernel.org, tglx@linutronix.de, hpa@zytor.com, akpm@linux-foundation.org, stable@vger.kernel.org, len.brown@intel.com, anhua.xu@intel.com, chaohong.guo@intel.com, Youquan Song Subject: Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken References: <1326099367-4166-1-git-send-email-youquan.song@intel.com> <1326103578.2442.50.camel@twins> <20120110001445.GA20542@linux-youquan.bj.intel.com> <1326107156.2442.59.camel@twins> <20120110055856.GA23741@linux-youquan.bj.intel.com> <1326153163.2366.7.camel@sbsiddha-mobl2> <20120110091805.GA28024@elte.hu> <4F0C4BF0.9090809@linux.intel.com> <1326206478.2442.111.camel@twins> In-Reply-To: <1326206478.2442.111.camel@twins> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: On 1/10/2012 6:41 AM, Peter Zijlstra wrote: > On Tue, 2012-01-10 at 06:32 -0800, Arjan van de Ven wrote: >> >> a very good default would be to keep all tasks on one package until half >> the cores in the package are busy, and then start spreading out. > > Does that still make sense when there's strong NUMA preference? By > forcing stuff on a single package you increase the number of remote > memory fetches (which generally generate more stalls), also the memory > controllers need to stay awake anyway. the memory controllers need to stake regardless of what you do; it's more a memory bandwidth kind of thing. if you have an enormous numa factor (>= 10 or so), then you really need a completely different policy I suspect. Thankfully those are rare.