From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753277Ab0AROdb (ORCPT ); Mon, 18 Jan 2010 09:33:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752890Ab0AROda (ORCPT ); Mon, 18 Jan 2010 09:33:30 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:41057 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752850Ab0AROda (ORCPT ); Mon, 18 Jan 2010 09:33:30 -0500 Subject: Re: [PATCH] perf_events: improve x86 event scheduling (v5) From: Peter Zijlstra To: Stephane Eranian Cc: Frederic Weisbecker , linux-kernel@vger.kernel.org, mingo@elte.hu, paulus@samba.org, davem@davemloft.net, perfmon2-devel@lists.sf.net, eranian@gmail.com In-Reply-To: References: <4b5430c6.0f975e0a.1bf9.ffff85fe@mx.google.com> <20100118134324.GB10364@nowhere> <1263822898.4283.558.camel@laptop> Content-Type: text/plain; charset="UTF-8" Date: Mon, 18 Jan 2010 15:33:03 +0100 Message-ID: <1263825183.4283.593.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2010-01-18 at 15:12 +0100, Stephane Eranian wrote: > > That said you do have a point, maybe we can express this particular > > thing differently.. maybe a pre and post group call like: > > > > void hw_perf_group_sched_in_begin(struct pmu *pmu) > > int hw_perf_group_sched_in_end(struct pmu *pmu) > > > The issue with hw_perf_group_sched_in() is that because we do not know > when we are done scheduling, we have to defer actual activation until > hw_perf_enable(). But we have to still mark the events as ACTIVE, > otherwise things go wrong in the generic layer and for non-PMU events. > That leads to partial duplication of event_sched_in()/event_sched_out() > in the PMU specific layer. > > As Frederic pointed out, the more natural way would be to simply rely > on event_sched_in()/event_sched_out() and the rollback logic and just > drop hw_perf_group_sched_in() which is there as an optimization and > not for correctness. Scheduling can be done incrementally from the > event_sched_in() function. > > > That way we know we need to track more state for rollback and can give > > the pmu implementation leeway to delay scheduling/availablility tests. > > > Rollback would still be handled by the generic code, wouldn't it? I'm not sure I understand your reply. Sure dropping hw_perf_group_sched_in() is still correct, but its also less optimal, since we have to determine schedulability for each incremental event.