Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752720AbdCMLQX (ORCPT ); Mon, 13 Mar 2017 07:16:23 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:59010 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752510AbdCMLQI (ORCPT ); Mon, 13 Mar 2017 07:16:08 -0400 Subject: Re: [PATCH v2 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src To: Peter Zijlstra References: <1488796993-25495-1-git-send-email-maddy@linux.vnet.ibm.com> <1488796993-25495-2-git-send-email-maddy@linux.vnet.ibm.com> <20170306112228.GZ6515@twins.programming.kicks-ass.net> <2fc7e466-1675-ef27-b820-ef33ed0be7da@linux.vnet.ibm.com> <20170307102359.GE6515@twins.programming.kicks-ass.net> Cc: mpe@ellerman.id.au, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Sukadev Bhattiprolu , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Wang Nan , Alexei Starovoitov , Stephane Eranian From: Madhavan Srinivasan Date: Mon, 13 Mar 2017 16:45:51 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <20170307102359.GE6515@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17031311-0004-0000-0000-0000054EC301 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17031311-0005-0000-0000-0000134B7480 Message-Id: <78c1b95d-2e82-f998-74ba-ebb1fdf5bb45@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-03-13_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1703130092 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1512 Lines: 37 On Tuesday 07 March 2017 03:53 PM, Peter Zijlstra wrote: > On Tue, Mar 07, 2017 at 03:28:17PM +0530, Madhavan Srinivasan wrote: >> >> On Monday 06 March 2017 04:52 PM, Peter Zijlstra wrote: >>> On Mon, Mar 06, 2017 at 04:13:08PM +0530, Madhavan Srinivasan wrote: >>>> From: Sukadev Bhattiprolu >>>> >>>> perf_mem_data_src is an union that is initialized via the ->val field >>>> and accessed via the bitmap fields. For this to work on big endian >>>> platforms, we also need a big-endian represenation of perf_mem_data_src. >>> Doesn't this break interpreting the data on a different endian machine? >> IIUC, we will need this patch to not to break the interpreting data >> on a different endian machine. Data collected from power8 LE/BE >> guests with this patchset applied. Kindly correct me if I missed >> your question here. > So your patch adds compile time bitfield differences. My worry was that > there was no dynamic conversion routine in the tools (it has for a lot > of other places). > > This yields two questions: > > - are these two static layouts identical? (seeing that you illustrate > cross-endian things working this seems likely). > > - should you not have fixed this in the tool only? This patch > effectively breaks ABI on big-endian architectures. IIUC, we are the first BE user for this feature (Kindly correct me if I am wrong), so technically we are not breaking ABI here :) . But let me also look at the dynamic conversion part. Maddy >