Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755856AbaJHKxH (ORCPT ); Wed, 8 Oct 2014 06:53:07 -0400 Received: from mail-wg0-f51.google.com ([74.125.82.51]:55895 "EHLO mail-wg0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755474AbaJHKxF (ORCPT ); Wed, 8 Oct 2014 06:53:05 -0400 Date: Wed, 8 Oct 2014 11:53:01 +0100 From: Matt Fleming To: Peter Zijlstra Cc: Ingo Molnar , Jiri Olsa , Arnaldo Carvalho de Melo , Thomas Gleixner , linux-kernel@vger.kernel.org, "H. Peter Anvin" , Matt Fleming , Arnaldo Carvalho de Melo Subject: Re: [PATCH 09/11] perf/x86/intel: Implement LRU monitoring ID allocation for CQM Message-ID: <20141008105301.GQ14343@console-pimps.org> References: <1411567455-31264-1-git-send-email-matt@console-pimps.org> <1411567455-31264-10-git-send-email-matt@console-pimps.org> <20141008095109.GD4750@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141008095109.GD4750@worktop.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 Wed, 08 Oct, at 11:51:09AM, Peter Zijlstra wrote: > On Wed, Sep 24, 2014 at 03:04:13PM +0100, Matt Fleming wrote: > > From: Matt Fleming > > > > It's possible to run into issues with re-using unused monitoring IDs > > because there may be stale cachelines associated with that ID from a > > previous allocation. This can cause the LLC occupancy values to be > > inaccurate. > > > > To attempt to mitigate this problem we place the IDs on a least recently > > used list, essentially a FIFO. The basic idea is that the longer the > > time period between ID re-use the lower the probability that stale > > cachelines exist in the cache. > > Do we want to provide a user configurable minumum guaranteed queue time? Potentially, yeah. That might be better suited as part of the final patch that includes the rotation code, which already has a delayed workqueue. We could add a minimum queue time before we start querying whether the data occupancy value for an RMID has dropped to zero on all sockets. That'd save us from an expensive smp_call_function_many() when we're unlikely to succeed anyway. -- Matt Fleming, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/