From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753661AbdEGW5O (ORCPT ); Sun, 7 May 2017 18:57:14 -0400 Received: from mail-it0-f43.google.com ([209.85.214.43]:35954 "EHLO mail-it0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750935AbdEGW5N (ORCPT ); Sun, 7 May 2017 18:57:13 -0400 MIME-Version: 1.0 X-Originating-IP: [2a02:168:5640:0:960b:2678:e223:c1c6] In-Reply-To: References: From: Daniel Vetter Date: Sun, 7 May 2017 14:33:15 +0200 X-Google-Sender-Auth: uWwpxGWTGPgpvUZW1Apc4i2dL50 Message-ID: Subject: Re: [git pull] drm pull for v4.12 To: Linus Torvalds Cc: Dave Airlie , Daniel Vetter , Jani Nikula , Maarten Lankhorst , =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , LKML , dri-devel 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 Sat, May 6, 2017 at 10:02 PM, Linus Torvalds wrote: > On Tue, May 2, 2017 at 8:44 PM, Dave Airlie wrote: >> i915: >> vblank evasion improvements > > These may be "improvements", but they end up being very noisy. > > I geta fair amount of messages like > > [drm] Atomic update on pipe (A) took 161 us, max time under evasion is 100 us > > on my desktop (i7-6700K) and I've seen it once on my laptop (i7-6560U) too. > > The commit message says "This will make it easier to find cases where > we potentially miss vblanks." but I'm not sure how that is the case. > There's nothing else helpful in the log, and it doesn't seem to be > associated with anything in particular (I'm just at the desktop, > running a few xterms and google-chrome). We did improve evasion a lot to the point that it didn't show up in our CI machines anymore (and we have a pile of those crunching tests 24/7), so we felt we could risk enabling this everywhere. But of course it pops up all over the place as soon as drm-next hits mainline, so we'll shut it down again except when debugging is enabled (to make sure we catch regressions in our CI). The evasion stuff is duct-tape around hw design issues and mostly harmless (i.e. very unlikely it'll result in a real issue for you, especially on normal Linux desktops that don't use overlay planes) if you hit it, worst case should be flickering or some other temporary visual corruptions. And the message happens when there's simply a potential for a miss, not when we observed the race happening (i.e. like lockdep splats about theoretical stuff). -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch