From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 329E1C4321D for ; Mon, 20 Aug 2018 14:36:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DFAB621531 for ; Mon, 20 Aug 2018 14:36:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DFAB621531 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727015AbeHTRwB (ORCPT ); Mon, 20 Aug 2018 13:52:01 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:38576 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726010AbeHTRwB (ORCPT ); Mon, 20 Aug 2018 13:52:01 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 37A43ED1; Mon, 20 Aug 2018 07:36:07 -0700 (PDT) Received: from [10.37.9.177] (unknown [10.37.9.177]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B68963F24A; Mon, 20 Aug 2018 07:36:02 -0700 (PDT) Subject: Re: [PATCH v3 0/7] perf: Add ioctl for PMU driver configuration To: Kim Phillips Cc: Mathieu Poirier , Will Deacon , Peter Zijlstra , Arnaldo Carvalho de Melo , Ingo Molnar , Thomas Gleixner , Alexander Shishkin , schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, Mark Rutland , Jiri Olsa , Namhyung Kim , Adrian Hunter , ast@kernel.org, Greg KH , "H. Peter Anvin" , suzuki.poulosi@arm.com, linux-s390@vger.kernel.org, Linux Kernel Mailing List , linux-arm-kernel References: <1531950487-24554-1-git-send-email-mathieu.poirier@linaro.org> <20180813124642.3d49c082a95fc294d926016e@arm.com> <20180814120910.ed225bbc462c58b09e5d68de@arm.com> <20180815093912.GE2427@arm.com> <20180815102820.3520d0c3875d2fd82300cdef@arm.com> <18fe78a3-9a58-cecd-ddb9-d46cbc473b95@arm.com> <20180820092252.32dd015afcc5cbf2fe4c7ab7@arm.com> From: Suzuki K Poulose Message-ID: Date: Mon, 20 Aug 2018 15:36:47 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180820092252.32dd015afcc5cbf2fe4c7ab7@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/20/2018 03:22 PM, Kim Phillips wrote: > On Mon, 20 Aug 2018 11:03:03 +0100 > Suzuki K Poulose wrote: > >> On 08/16/2018 08:28 PM, Mathieu Poirier wrote: >>> On Wed, 15 Aug 2018 at 09:28, Kim Phillips wrote: >>>> >>>> On Wed, 15 Aug 2018 10:39:13 +0100 >>>> Will Deacon wrote: >>>> >>>>> On Tue, Aug 14, 2018 at 01:42:27PM -0600, Mathieu Poirier wrote: >>>>>> On Tue, 14 Aug 2018 at 11:09, Kim Phillips wrote: >>>>>>> The other thing that's going on here is that I'm becoming numb to the >>>>>>> loathsome "failed to mmap with 12 (Cannot allocate memory)" being >>>>>>> returned no matter what the error is/was. E.g., an error that would >>>>>>> indicate a sense of non-implementation would be much better >>>>>>> appreciated than presumably what the above is doing, i.e., returning >>>>>>> -ENOMEM. That, backed up with specific details in the form of human >>>>>>> readable text in dmesg would be *most* welcome. >>>>>> >>>>>> As part of the refactoring of the code to support CPU-wide scenarios I >>>>>> intend to emit better diagnostic messages from the driver. Modifying >>>>>> rb_alloc_aux() to propagate the error message generated by the >>>>>> architecture specific PMUs doesn't look hard either and I _may_ get to >>>>>> it as part of this work. >>>>> >>>>> For the record, I will continue to oppose PMU drivers that dump diagnostics >>>>> about user-controlled input into dmesg, but the coresight drivers are yours >>>>> so it's up to you and I won't get in the way! >>>> >>>> That sounds technically self-contradicting to me. Why shouldn't >>>> coresight share the same policies as those used for PMU drivers? Or >>>> why not allow the individual vendor PMU driver authors control the >>>> level of user-friendliness of their own drivers? >>>> >>>> That being said, Matheiu, would you accept patches that make coresight >>>> more verbose in dmesg? >>> >>> It depends on the issue you're hoping to address. I'd rather see the >>> root cause of the problem fixed than adding temporary code. Suzuki >>> added the ETR perf API and I'm currently working on CPU-wide >>> scenarios. From there and with regards to what can happen in >>> setup_aux(), we should have things covered. >> >> I think the main issue is the lack of error code propagation from >> setup_aux() back to the perf_aux_output_handle_begin(), which always >> return -ENOMEM. If we fix that, we could get better idea of whats >> wrong. > > Why get a better idea when we can get the exact details? The different values for error numbers are there for a reason... > >> If someone is planning to add verbose messages, they may do so by adding >> dev_dbg() / pr_debug(), which can be turned on as and when needed. > > I disagree: that just adds another usage and kernel configuration > obstacle. Why not use pr_err straight up? I personally don't agree to usage of pr_err() in paths which are easily triggered from user input. Also, we are moving all the "debugging" messages to the dynamic debug, to prevent lockdep splats. Suzuki