From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932561Ab0DGL6u (ORCPT ); Wed, 7 Apr 2010 07:58:50 -0400 Received: from mail-fx0-f223.google.com ([209.85.220.223]:33184 "EHLO mail-fx0-f223.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756923Ab0DGL6r (ORCPT ); Wed, 7 Apr 2010 07:58:47 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=lzRsy+HmgKKhZwuxtxy7WvCz+xOLlGku+7t/N87PdxxtAKKxnQCG27MmTZzYRI8dBh zJW4FwiZtUT/wv85EM9oztrALMReoaFuseG7N9Kz6mPF3dPAL0QOQW/4mwSUagBJjbOb aMYfAIBCY7KlHY27NXSAQHJ6dhDIT75dGhbYo= Date: Wed, 7 Apr 2010 13:58:41 +0200 From: Frederic Weisbecker To: Peter Zijlstra Cc: Ingo Molnar , LKML , Arnaldo Carvalho de Melo , Paul Mackerras Subject: Re: [PATCH] perf: Store active software events in a hashlist Message-ID: <20100407115839.GE5143@nowhere> References: <1270476502-6214-1-git-send-regression-fweisbec@gmail.com> <1270567653.20295.11.camel@laptop> <1270631093.5109.569.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1270631093.5109.569.camel@twins> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 07, 2010 at 11:04:53AM +0200, Peter Zijlstra wrote: > On Tue, 2010-04-06 at 17:27 +0200, Peter Zijlstra wrote: > > 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. > > Alternatively, you can simply but the hash table into the per-cpu > structure and not allocate it, its only a single page (half a page if > you use 32bit or actually use 8 bits. As you prefer. This would indeed make it more simple, but that would also make these pages unused most of the time.