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 0B153C4321D for ; Mon, 20 Aug 2018 15:25:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B796F2154B for ; Mon, 20 Aug 2018 15:25:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B796F2154B 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 S1727259AbeHTSlk (ORCPT ); Mon, 20 Aug 2018 14:41:40 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:39320 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726021AbeHTSlk (ORCPT ); Mon, 20 Aug 2018 14:41:40 -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 3EF60ED1; Mon, 20 Aug 2018 08:25:35 -0700 (PDT) Received: from dupont (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 22A523F24A; Mon, 20 Aug 2018 08:25:34 -0700 (PDT) Date: Mon, 20 Aug 2018 10:25:32 -0500 From: Kim Phillips To: Suzuki K Poulose Cc: Mathieu Poirier , Will Deacon , Peter Zijlstra , Arnaldo Carvalho de Melo , Ingo Molnar , Thomas Gleixner , Alexander Shishkin , , , Mark Rutland , Jiri Olsa , Namhyung Kim , Adrian Hunter , , Greg KH , "H. Peter Anvin" , , , Linux Kernel Mailing List , linux-arm-kernel Subject: Re: [PATCH v3 0/7] perf: Add ioctl for PMU driver configuration Message-Id: <20180820102532.96a90fe59d9ea3785df76a4d@arm.com> In-Reply-To: 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> Organization: Arm X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 20 Aug 2018 15:36:47 +0100 Suzuki K Poulose wrote: > 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... But the same error number, e.g., EINVAL, can be returned for different reasons. > >> 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. Why not? pr_* are ratelimited. > Also, we are moving all the "debugging" > messages to the dynamic debug, to prevent lockdep splats. Are you referring to this?: https://lkml.org/lkml/2018/5/1/73 Re-reading the thread, AFAICT, it was never proven that the splats occurred due to the dev_infos, and there's no dev_info in this stacktrace: https://lkml.org/lkml/2018/5/10/269 But even if it were, wouldn't the splats also occur with dev_dbg? Kim