From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758205AbbAIPbj (ORCPT ); Fri, 9 Jan 2015 10:31:39 -0500 Received: from mail-wg0-f51.google.com ([74.125.82.51]:64557 "EHLO mail-wg0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932991AbbAIPYq (ORCPT ); Fri, 9 Jan 2015 10:24:46 -0500 Date: Fri, 9 Jan 2015 15:24:42 +0000 From: Matt Fleming To: Peter Zijlstra 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: <20150109152442.GG495@console-pimps.org> References: <1415999712-5850-1-git-send-email-matt@console-pimps.org> <1415999712-5850-11-git-send-email-matt@console-pimps.org> <20150106171712.GH3337@twins.programming.kicks-ass.net> <20150109121401.GB495@console-pimps.org> <20150109130250.GH29390@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150109130250.GH29390@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 09 Jan, at 02:02:50PM, Peter Zijlstra wrote: > On Fri, Jan 09, 2015 at 12:14:01PM +0000, Matt Fleming wrote: > > On Tue, 06 Jan, at 06:17:12PM, Peter Zijlstra wrote: > > > > > > afaict the again label will try and steal yet another rmid, if rmids > > > don't decay fast enough, we could end up with all rmids on the limbo > > > list and none active. Or am I missing something here? > > > > You're not missing anything, that's true, we will try and steal more > > RMIDs. We could perhaps put a limit on how many RMIDs we're willing to > > steal, but I think it should definitely be > 1 because RMIDs can > > stabilize out of order. > > > > It's worth pointing out that we only steal more RMIDs if the ones on the > > limbo list have been queued for the "minimum queue time" - it really is > > a last resort. > > Do we really care? Why not just hold up everything until the one(s) we > have are low enough? > > Yes it all blows, but would not some active be better than none active, > just because the stupid lines aren't clearing fast enough? Right, but now we need a "steal limit", so we know when to stop stealing active RMIDs. (cqm_max_rmid + 1) / 4 ? I guess any limit is better than no limit. -- Matt Fleming, Intel Open Source Technology Center