From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757218AbbAIM6u (ORCPT ); Fri, 9 Jan 2015 07:58:50 -0500 Received: from casper.infradead.org ([85.118.1.10]:52586 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752146AbbAIM6t (ORCPT ); Fri, 9 Jan 2015 07:58:49 -0500 Date: Fri, 9 Jan 2015 13:58:29 +0100 From: Peter Zijlstra To: Matt Fleming Cc: Ingo Molnar , Jiri Olsa , Arnaldo Carvalho de Melo , Andi Kleen , Thomas Gleixner , linux-kernel@vger.kernel.org, "H. Peter Anvin" , Kanaka Juvva , Matt Fleming Subject: Re: [PATCH v4 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs Message-ID: <20150109125829.GF29390@twins.programming.kicks-ass.net> References: <1415999712-5850-1-git-send-email-matt@console-pimps.org> <1415999712-5850-11-git-send-email-matt@console-pimps.org> <20150107121617.GF25325@worktop.programming.kicks-ass.net> <20150109125507.GD495@console-pimps.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150109125507.GD495@console-pimps.org> 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 Fri, Jan 09, 2015 at 12:55:07PM +0000, Matt Fleming wrote: > On Wed, 07 Jan, at 01:16:17PM, Peter Zijlstra wrote: > > On Fri, Nov 14, 2014 at 09:15:11PM +0000, Matt Fleming wrote: > > + /* > > > + * A reasonable upper limit on the max threshold is the number > > > + * of lines tagged per RMID if all RMIDs have the same number of > > > + * lines tagged in the LLC. > > > + * > > > + * For a 35MB LLC and 56 RMIDs, this is ~1.8% of the LLC. > > > + */ > > > + __intel_cqm_max_threshold = > > > + boot_cpu_data.x86_cache_size * 1024 / (cqm_max_rmid + 1); > > > > Seeing how a percentage is without unit, the 35MB figure seems > > pointless. > > It's only an example to demonstrate that this fudge calculation makes > sense on the current class of CQM-enabled hardware. > > > Also, why would a flat distribution be a good measure for 'empty'? I > > would think that would in fact constitute in use. > > It's not, it's a good measure for 'full'. This is the *max* threshold. > When searching for RMIDs to stabilize we'll stop searching if > __intel_cqm_threshold == __intel_cqm_max_threshold, since that indicates > all our RMIDs have *so* many lines tagged that it's unlikely increasing > __intel_cqm_threshold any further would be a win. Right, but we'll also consider RMIDs with less than this as fit for reuse. So we'll re-use RMIDs that are effectively full. Our aim is to acquire an 'empty' RMID, not give up and start reusing full ones just because, right?