From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933675AbdA0RSk (ORCPT ); Fri, 27 Jan 2017 12:18:40 -0500 Received: from mail-yw0-f170.google.com ([209.85.161.170]:35899 "EHLO mail-yw0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933525AbdA0RRy (ORCPT ); Fri, 27 Jan 2017 12:17:54 -0500 MIME-Version: 1.0 In-Reply-To: <87h94kbt29.fsf@ashishki-desk.ger.corp.intel.com> References: <20170126094057.13805-1-alexander.shishkin@linux.intel.com> <20170126094057.13805-2-alexander.shishkin@linux.intel.com> <20170126182645.GA1991@linaro.org> <87h94kbt29.fsf@ashishki-desk.ger.corp.intel.com> From: Mathieu Poirier Date: Fri, 27 Jan 2017 10:17:53 -0700 Message-ID: Subject: Re: [PATCH 1/3] perf, pt, coresight: Clean up address filter structure To: Alexander Shishkin Cc: Peter Zijlstra , Ingo Molnar , "linux-kernel@vger.kernel.org" , Vince Weaver , Stephane Eranian , Arnaldo Carvalho de Melo , Will Deacon , Mark Rutland Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 27 January 2017 at 05:12, Alexander Shishkin wrote: > Mathieu Poirier writes: > >> Hi Alex, > > Hi Mathieu, > >> This changes the behavior we used to have. Now a range filter with a size of 0 >> will be treated as start filter rather than an error. See below on a possible >> way of fixing this. > > Not really. Currently we have 2 drivers using this and both reject the > type=range&&size==0 filters with either -EOPNOTSUPP or -EINVAL. With > this change, PT will still reject it as it doesn't support single > address triggers, but Coresight will treat it as if it was a single > address filter. Hence my statement about a change in behaviour. > Which makes sense, because that's what a range of size > zero is. Note, that a range that covers one instruction has to be at > least size==1 (and I'm guessing size==4 for Coresight, but I may be > wrong). > > So yes, this does change the existing behavior, but in doing so it > removes the ambiguity of zero sized ranges. Specifying a size of zero with a range filter is wrong and as such should be treated as an error, which is what the current code is doing. If people want a start filter they can use the syntax required for that. In my opinion treating a range filter with a size zero as a start filter is adding intelligence to the machine, something that should probably be avoided. > >> if (filter->action == PERF_ADDR_FILTER_ACTION_RANGE) > > But "range" is not an action, it's a type of a filter. It determines the > condition that triggers an action. An action, however, is what we do > when the condition comes true. Then filter->action could be renamed 'type'. In the end filters on PT are range filters, the same way they are on CS. But changing the naming convention is a matter of personal opinion - I am fine with what we currently have. On the flip side reordering the fields in the 'if_tokens' match table would allow to set the filters properly in perf_event_parse_addr_filter(), keep the current behaviour intact and get rid of filter->range. Thanks, Mathieu > > Regards, > -- > Alex