From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH 1/3] perf: add context field to perf_event Date: Mon, 11 Jul 2011 22:07:53 +0100 Message-ID: <20110711210753.GA3582@e102144-lin.cambridge.arm.com> References: <1309362157-6596-1-git-send-email-avi@redhat.com> <1309362157-6596-2-git-send-email-avi@redhat.com> <20110629160841.GA2032@somewhere> <20110629162725.GH15521@e102144-lin.cambridge.arm.com> <20110704135820.GD5551@somewhere> <4E11C9CC.2070909@redhat.com> <20110704143655.GE5551@somewhere> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , Ingo Molnar , "a.p.zijlstra@chello.nl" , "acme@ghostprotocols.net" , Jason Wessel To: Frederic Weisbecker Return-path: Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:37588 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753875Ab1GKVIU (ORCPT ); Mon, 11 Jul 2011 17:08:20 -0400 Content-Disposition: inline In-Reply-To: <20110704143655.GE5551@somewhere> Sender: kvm-owner@vger.kernel.org List-ID: On Mon, Jul 04, 2011 at 03:36:57PM +0100, Frederic Weisbecker wrote: > On Mon, Jul 04, 2011 at 05:10:20PM +0300, Avi Kivity wrote: > > On 07/04/2011 04:58 PM, Frederic Weisbecker wrote: > > >Another thing I would like to do in the even longer term is to not use perf anymore > > >for ptrace breakpoints, because that involves a heavy dependency and few people are > > >happy with that. Instead we should just have a generic hook into the sched_switch() > > >and handle pure ptrace breakpoints there. The central breakpoint API would still be > > >there to reserve/schedule breakpoint resources between ptrace and perf. > > > > > > > 'struct preempt_notifier' may be the hook you're looking for. > > Yeah looks like a perfect fit as it's per task. I had a quick look at this and I think the preempt_notifier stuff needs slightly extending so that we can register a notifier for a task other than current [e.g. the child of current on which we are installing breakpoints]. If the task in question is running, it looks like this will introduce a race condition between notifier registration and rescheduling. For the purposes of ptrace this shouldn't be a problem as the child will be stopped, but others might also want to make use of the new functionality. Any ideas on how this could be achieved, or am I better off just restricting this to children that are being traced? Cheers, Will