linux-kernel - Re: [PATCH] drm/i915: Make vblank evade warnings optional

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Date:   Mon, 8 May 2017 09:25:36 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        "Syrjala, Ville" <ville.syrjala@...ux.intel.com>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Dave Airlie <airlied@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Subject: Re: [PATCH] drm/i915: Make vblank evade warnings optional

On Sun, May 07, 2017 at 07:52:14PM -0600, Jens Axboe wrote:
> On 05/07/2017 11:56 AM, Daniel Vetter wrote:
> > On Sun, May 7, 2017 at 7:46 PM, Jens Axboe <axboe@...nel.dk> wrote:
> >> On 05/07/2017 11:12 AM, ville.syrjala@...ux.intel.com wrote:
> >>> From: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> >>>
> >>> Add a new Kconfig option to enable/disable the extra warnings
> >>> from the vblank evade code. For now we'll keep the warning
> >>> about an actually missed vblank always enabled as that can have
> >>> an actual user visible impact. But if we miss the deadline
> >>> othrwise there's no real need to bother the user with that.
> >>> We'll want these warnings enabled during development however
> >>> so that we can catch regressions.
> >>>
> >>> Based on the reports it looks like this is still very easy
> >>> to hit on SKL, so we have more work ahead of us to optimize
> >>> the crtiical section further.
> >>
> >> Shouldn't it just be a debug printk or something instead, so that normal
> >> people don't see it, but the folks that turn on debugging can get the
> >> info they need? Seems silly to add a kconfig option for this.
> > 
> > I guess we could keep it as debug for users, but we want to make this
> > a hard failure on our CI machines. Kconfig knob is the easiest to roll
> > out to all machines.
> 
> Wouldn't a module parameter be more useful then, as an opt-in
> to catch these violations.
> 
> Nobody is going to know wtf to set this kconfig option to.

They're all hidden behind an overall i915 debugging option which tells you
not to enable it. You won't see this.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch