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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 5F262C33CB1 for ; Wed, 15 Jan 2020 14:21:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2AD632084D for ; Wed, 15 Jan 2020 14:21:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=poorly.run header.i=@poorly.run header.b="Fyez2ljB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726506AbgAOOVU (ORCPT ); Wed, 15 Jan 2020 09:21:20 -0500 Received: from mail-yb1-f194.google.com ([209.85.219.194]:37273 "EHLO mail-yb1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726501AbgAOOVU (ORCPT ); Wed, 15 Jan 2020 09:21:20 -0500 Received: by mail-yb1-f194.google.com with SMTP id o199so2940976ybc.4 for ; Wed, 15 Jan 2020 06:21:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=poorly.run; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=3ObquDazAteZHqeIwUV/wupCgwXXwnvtoRKdROHL06M=; b=Fyez2ljB74T5rwo/zJO7JOoMGJwoPpEs/0jNr6ETdoOXZMPSEjDkKjkubY7TzGs9ug WlGGBOODv9KPiK8JZtMAkUaFz5NBYvxieGCffYyEt0ZwYXMda/4uOmR5HguLtNffosbt w2UvHFJVASvN3qOOo0PfjwM+NnaTo9D+b0/TotySDydAVBeRZZdsm1bSgV2pw5JaHC2p Or9TuNWaL0dtYNDXfxaZOs6mv3fC1cGgy1PBNt3b3fxi4WF5F52X5QuDRVOdtdBIZT55 Hv4APhbS84NaPVXO8KgDUaHLZgR3W/sx+QIA4hHCoaojZkz9/8nnut8ZiW9D24d/rcTK E5kA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=3ObquDazAteZHqeIwUV/wupCgwXXwnvtoRKdROHL06M=; b=h+AZZ4WtG/aualnfoNt1gj4xVGM68+yfUg8/dT4ORJbL21ktsALec/wrLVgohUFHsO N/doPeICoMoVzza/fNekseLkasLCgNamTCM9Au7tCPhg4HP0zOdDGl5gWhVKUu9OWg7B GF+K5Dqh3uxrqaHdg4EzJmDIsq52eAU6EeUvjxo/IDyeJXXeUdoC6VoQ1Oi7kcXeoPgF GvzaUn+2drRnrNHKSXYi1iwhJgirlCSD3k0CkfB7SFgduHwK/4s868PKKs34Zp/vdeWf gt2fR4IfT1abG5Z8pNI/LjEgSjgML/f/JF9Xop7nMcpjxCHx+PyRBnTB7KUxHj1Y9ewh B5Ng== X-Gm-Message-State: APjAAAW+rkFp+N1EDlU8wGS94n8AjH4PIMDYykNHzhVDKt6rKubR3YeN DwanW7dJRBL1J3//vykWRUb+9A== X-Google-Smtp-Source: APXvYqyOsPXQ1DEc7nSX1QdY8Nfs6hxA8MMMSaVb01nV96cXhb/yL7axeWHdvpfTDAUsr8WEyou6PA== X-Received: by 2002:a25:743:: with SMTP id 64mr21908668ybh.178.1579098079461; Wed, 15 Jan 2020 06:21:19 -0800 (PST) Received: from localhost ([2620:0:1013:11:1e1:4760:6ce4:fc64]) by smtp.gmail.com with ESMTPSA id z12sm7961758ywl.27.2020.01.15.06.21.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jan 2020 06:21:18 -0800 (PST) Date: Wed, 15 Jan 2020 09:21:18 -0500 From: Sean Paul To: Chris Wilson Cc: Sean Paul , dri-devel@lists.freedesktop.org, Jonathan Corbet , David Airlie , Daniel Vetter , linux-doc@vger.kernel.org, Sean Paul , Steven Rostedt , Thomas Zimmermann Subject: Re: [PATCH v4] drm/trace: Buffer DRM logs in a ringbuffer accessible via debugfs Message-ID: <20200115142118.GD25564@art_vandelay> References: <20200114172155.215463-1-sean@poorly.run> <157908459623.12549.3531242692320169983@skylake-alporthouse-com> <20200115134158.GC25564@art_vandelay> <157909687975.14122.1932646175287417072@skylake-alporthouse-com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <157909687975.14122.1932646175287417072@skylake-alporthouse-com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, Jan 15, 2020 at 02:01:19PM +0000, Chris Wilson wrote: > Quoting Sean Paul (2020-01-15 13:41:58) > > On Wed, Jan 15, 2020 at 10:36:36AM +0000, Chris Wilson wrote: > > > Quoting Sean Paul (2020-01-14 17:21:43) > > > > From: Sean Paul > > > > > > > > This patch uses a ring_buffer to keep a "flight recorder" (name credit Weston) > > > > of DRM logs for a specified set of debug categories. The user writes a > > > > bitmask of debug categories to the "trace_mask" node and can read log > > > > messages from the "trace" node. > > > > > > > > These nodes currently exist in debugfs under the dri directory. I > > > > intended on exposing all of this through tracefs originally, but the > > > > tracefs entry points are not exposed, so there's no way to create > > > > tracefs files from drivers at the moment. I think it would be a > > > > worthwhile endeavour, but one requiring more time and conversation to > > > > ensure the drm traces fit somewhere sensible. > > > > > > Fwiw, I have a need for client orientated debug message store, with > > > the primary purpose of figuring out -EINVAL. We need per-client so we can > > > put sensitive information about the potentially buggy client behaviour, > > > and of course it needs to be accessible by the non-privileged client. > > > > > > On the execution side, it's easy to keep track of the client so we could > > > trace execution flow per client, within reason. And we could do > > > similarly for kms clients. > > > > Could you build such a thing with drm_trace underpinning it, just put the > > pertinent information in the message? > > Not as is. The global has to go, and there's no use for debugfs. So we > are just left with a sprintf() around a ring_buffer. I am left in the > same position as just wanting to generalise tracek to take the ringbuffer > as a parameter. > Ah, I think I see what you're getting at now. I think it would be reasonable to split out a drm_trace_buffer from the current code for this purpose. We could have an interface like: struct drm_trace_buffer *drm_trace_buffer_init(unsigned int num_pages); int drm_trace_buffer_resize(struct drm_trace_buffer *buf, unsigned int num_pages); int drm_trace_buffer_printf(struct drm_trace_buffer *buf, const char *format, ...); int drm_trace_buffer_output(struct seq_file *seq); void drm_trace_buffer_cleanup(struct drm_trace_buffer *buf); Then to Joonas' point, we could have drm_trace_log which uses this interface to mirror the logs with a debugfs interface. Would that work for your purpose? > > > Just chiming to say, I don't think a duplicate of dmesg hidden inside > > > debugfs achieves much. But a generic tracek-esque ringbuf would be very > > > useful -- even if only so we can separate our GEM_TRACE from the global > > > tracek. > > > > I think that's essentially what we've got, I've just narrowly focused on > > surfacing debug logs. If drm_trace_printf were exported, replacing > > GEM_TRACE would be as simple as s/trace_printk/drm_trace_printf/. Initially I > > thought exporting it to drivers would be a bad idea, but I'm open to changing my > > mind on this as long as drivers are using it responsibly. > > I definitely can't make the mistake of flooding kms tracing with > overwhelming execution traces -- we can't go back to mixing kms traces > with execution traces. Yeah, I assumed this wouldn't be enabled during normal operation, just for debugging (as it is used now). Sean > -Chris -- Sean Paul, Software Engineer, Google / Chromium OS