From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754309AbaCRJRG (ORCPT ); Tue, 18 Mar 2014 05:17:06 -0400 Received: from merlin.infradead.org ([205.233.59.134]:54518 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752565AbaCRJRD (ORCPT ); Tue, 18 Mar 2014 05:17:03 -0400 Date: Tue, 18 Mar 2014 10:16:56 +0100 From: Peter Zijlstra To: Davidlohr Bueso Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, hpa@linux.intel.com, len.brown@intel.com, linux-tip-commits@vger.kernel.org Subject: Re: [tip:x86/urgent] x86 idle: Repair large-server 50-watt idle-power regression Message-ID: <20140318091656.GQ25546@laptop.programming.kicks-ass.net> References: <1395102010.2474.21.camel@buesod1.americas.hpqcorp.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1395102010.2474.21.camel@buesod1.americas.hpqcorp.net> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 17, 2014 at 05:20:10PM -0700, Davidlohr Bueso wrote: > On Thu, 2013-12-19 at 11:51 -0800, tip-bot for Len Brown wrote: > > Commit-ID: 40e2d7f9b5dae048789c64672bf3027fbb663ffa > > Gitweb: http://git.kernel.org/tip/40e2d7f9b5dae048789c64672bf3027fbb663ffa > > Author: Len Brown > > AuthorDate: Wed, 18 Dec 2013 16:44:57 -0500 > > Committer: H. Peter Anvin > > CommitDate: Thu, 19 Dec 2013 11:47:39 -0800 > > > > x86 idle: Repair large-server 50-watt idle-power regression > > FYI this commit can cause some non trivial performance regressions for > larger core count systems. While not surprising because of the nature of > the change, having intel_idle do more cacheline invalidations, I still > wanted to let you guys know. For instance, on a 160 core Westmere > system, aim7 throughput can go down in a number of tests, anywhere from > -10% to -25%. > > I guess it comes down to one of those performance vs energy things. And > sure, max_cstate can be set to overcome this, but it's still something > that was previously taken for granted. -10% to -25% seems a lot for a single cacheline flush. Also I would expect the expected idle time to be very short while running aim7. So could it be the cacheflush is actually taking longer than the expected idle time?