From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755422Ab0DFP1n (ORCPT ); Tue, 6 Apr 2010 11:27:43 -0400 Received: from casper.infradead.org ([85.118.1.10]:57623 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754730Ab0DFP1g (ORCPT ); Tue, 6 Apr 2010 11:27:36 -0400 Subject: Re: [PATCH] perf: Store active software events in a hashlist From: Peter Zijlstra To: Frederic Weisbecker Cc: Ingo Molnar , LKML , Arnaldo Carvalho de Melo , Paul Mackerras In-Reply-To: <1270476502-6214-1-git-send-regression-fweisbec@gmail.com> References: <1270476502-6214-1-git-send-regression-fweisbec@gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 06 Apr 2010 17:27:33 +0200 Message-ID: <1270567653.20295.11.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2010-04-05 at 16:08 +0200, Frederic Weisbecker wrote: > Each time a software event triggers, we need to walk through > the entire list of events from the current cpu and task contexts > to retrieve a running perf event that matches. > We also need to check a matching perf event is actually counting. > > This walk is wasteful and makes the event fast path scaling > down with a growing number of events running on the same > contexts. > > To solve this, we store the running perf events in a hashlist to > get an immediate access to them against their type:event_id when > they trigger. So we have a hash-table per-cpu, each event takes a ref on the hash table, when the thing is empty we free it. When the event->cpu == -1 (all cpus) we take a ref on all possible cpu's hash-table (should be online I figure, but that requires adding a hotplug handler). Then on event enable/disable we actually add the event to the hash-table belonging to the cpu the event/task gets scheduled on, since each event can only ever be active on one cpu. Right? So looks good, altough I think we want to do that online/hotplug thing.