From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 4/6] kvm tools: Add rwlock wrapper Date: Fri, 27 May 2011 13:24:43 +0200 Message-ID: <20110527112443.GA27397@elte.hu> References: <1306426743.3065.34.camel@lappy> <20110526180518.GA3572@elte.hu> <4DDE97CE.4000302@redhat.com> <20110526202531.GA2765@elte.hu> <20110526230508.GA15983@Krystal> <20110527102533.GA24608@elte.hu> <20110527110729.GA26920@elte.hu> <20110527111057.GA27058@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Pekka Enberg , Avi Kivity , Sasha Levin , john@jfloren.net, kvm@vger.kernel.org, asias.hejun@gmail.com, gorcunov@gmail.com, prasadjoshi124@gmail.com, "Paul E. McKenney" To: Mathieu Desnoyers Return-path: Received: from mx3.mail.elte.hu ([157.181.1.138]:57337 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752032Ab1E0LY7 (ORCPT ); Fri, 27 May 2011 07:24:59 -0400 Content-Disposition: inline In-Reply-To: <20110527111057.GA27058@elte.hu> Sender: kvm-owner@vger.kernel.org List-ID: * Ingo Molnar wrote: > Note that you do not want the context switch event, but the CPU > migration event: that will notify user-space when it gets migrated > to another CPU. This is the case that RCU really needs. Also note that the main current use-case of perf events is instrumentation, thus if you make use of this facility for user-space RCU you need to check whether the events are all precise and arrive in time to the target process, etc. Statistical behavior isnt a big problem for instrumentation but it's a showstopper for RCU, obviously! :-) If you find such bugs then we want to fix them, so there's no fundamental *desire* from us for these events to be statistical and inaccurate anywhere. Thanks, Ingo