Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754240AbbETQ2U (ORCPT ); Wed, 20 May 2015 12:28:20 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:39739 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751996AbbETQ2T (ORCPT ); Wed, 20 May 2015 12:28:19 -0400 Date: Wed, 20 May 2015 18:28:11 +0200 From: Peter Zijlstra To: Vince Weaver Cc: LKML , Stephane Eranian , Arnaldo Carvalho de Melo , Jiri Olsa , Ingo Molnar , Paul Mackerras Subject: Re: perf: odd event scheduling issue Message-ID: <20150520162811.GN18673@twins.programming.kicks-ass.net> References: <20150520070057.GK3644@twins.programming.kicks-ass.net> <20150520092842.GF18673@twins.programming.kicks-ass.net> <20150520135209.GI18673@twins.programming.kicks-ass.net> <20150520152534.GJ18673@twins.programming.kicks-ass.net> <20150520160802.GL18673@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150520160802.GL18673@twins.programming.kicks-ass.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 Content-Length: 1827 Lines: 46 On Wed, May 20, 2015 at 06:08:02PM +0200, Peter Zijlstra wrote: > @@ -2062,6 +2081,22 @@ intel_get_excl_constraints(struct cpu_hw_events *cpuc, struct perf_event *event, > */ > > /* > + * Do not allow scheduling of more than max_alloc_cntrs > + * which is set to half the available generic counters. > + * > + * This helps avoid counter starvation of sibling thread > + * by ensuring at most half the counters cannot be in > + * exclusive mode. There is not designated counters for the > + * limits. Any N/2 counters can be used. This helps with > + * events with specifix counter constraints > + */ > + if (xl->num_alloc_cntrs++ >= xl->max_alloc_cntrs) { > + /* wipe the GP counters */ > + cx->idxmsk64 &= ~((1ULL << INTEL_PMC_IDX_FIXED) - 1); > + goto done; > + } > + > + /* > * Modify static constraint with current dynamic > * state of thread > * While this improves things, its still sub optimal because we should only increase num_alloc_cntrs when we actually allocate a GP register, but we do that at commit time and that callback is too late to back out / retry. So ideally we'd move the callback into scheduling code, but that means we also have to move the xlo array into the sched_state etc. [ which brings me to the whole xl vs xlo thing, I think we done that the wrong way around. It would be more natural to account to xl and create constraints based on xlo. ] Secondly, we should only enforce this limit if and when there are exclusive events on the system I suppose. I have some ideas on how to go do this, but I need a break.. -- 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/