linux-kernel - Re: [Intel-gfx] [PATCH v7 0/9] dyndbg: drm.debug adaptation

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Message-ID: <Y1rllFeOnT9/PQVA@intel.com>
Date:   Thu, 27 Oct 2022 23:09:56 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     jim.cromie@...il.com
Cc:     Jason Baron <jbaron@...mai.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>, daniel.vetter@...ll.ch,
        intel-gfx@...ts.freedesktop.org, linux@...musvillemoes.dk,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        seanpaul@...omium.org, dri-devel@...ts.freedesktop.org,
        joe@...ches.com, intel-gvt-dev@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH v7 0/9] dyndbg: drm.debug adaptation

On Thu, Oct 27, 2022 at 01:55:39PM -0600, jim.cromie@...il.com wrote:
> On Thu, Oct 27, 2022 at 9:59 AM Ville Syrjälä
> <ville.syrjala@...ux.intel.com> wrote:
> >
> > On Thu, Oct 27, 2022 at 09:37:52AM -0600, jim.cromie@...il.com wrote:
> > > On Thu, Oct 27, 2022 at 9:08 AM Jason Baron <jbaron@...mai.com> wrote:
> > > >
> > > >
> > > >
> > > > On 10/21/22 05:18, Jani Nikula wrote:
> > > > > On Thu, 20 Oct 2022, Ville Syrjälä <ville.syrjala@...ux.intel.com> wrote:
> > > > >> On Sat, Sep 24, 2022 at 03:02:34PM +0200, Greg KH wrote:
> > > > >>> On Sun, Sep 11, 2022 at 11:28:43PM -0600, Jim Cromie wrote:
> > > > >>>> hi Greg, Dan, Jason, DRM-folk,
> > > > >>>>
> > > > >>>> heres follow-up to V6:
> > > > >>>>   rebased on driver-core/driver-core-next for -v6 applied bits (thanks)
> > > > >>>>   rework drm_debug_enabled{_raw,_instrumented,} per Dan.
> > > > >>>>
> > > > >>>> It excludes:
> > > > >>>>   nouveau parts (immature)
> > > > >>>>   tracefs parts (I missed --to=Steve on v6)
> > > > >>>>   split _ddebug_site and de-duplicate experiment (way unready)
> > > > >>>>
> > > > >>>> IOW, its the remaining commits of V6 on which Dan gave his Reviewed-by.
> > > > >>>>
> > > > >>>> If these are good to apply, I'll rebase and repost the rest separately.
> > > > >>>
> > > > >>> All now queued up, thanks.
> > > > >>
> > > > >> This stuff broke i915 debugs. When I first load i915 no debug prints are
> > > > >> produced. If I then go fiddle around in /sys/module/drm/parameters/debug
> > > > >> the debug prints start to suddenly work.
> > > > >
> > > > > Wait what? I always assumed the default behaviour would stay the same,
> > > > > which is usually how we roll. It's a regression in my books. We've got a
> > > > > CI farm that's not very helpful in terms of dmesg logging right now
> > > > > because of this.
> > > > >
> > > > > BR,
> > > > > Jani.
> > > > >
> > > > >
> > > >
> > > > That doesn't sound good - so you are saying that prior to this change some
> > > > of the drm debugs were default enabled. But now you have to manually enable
> > > > them?
> > > >
> > > > Thanks,
> > > >
> > > > -Jason
> > >
> > >
> > > Im just seeing this now.
> > > Any new details ?
> >
> > No. We just disabled it as BROKEN for now. I was just today thinking
> > about sending that patch out if no solutin is forthcoming soon since
> > we need this working before 6.1 is released.
> >
> > Pretty sure you should see the problem immediately with any driver
> > (at least if it's built as a module, didn't try builtin). Or at least
> > can't think what would make i915 any more special.
> >
> 
> So, I should note -
> 99% of my time & energy on this dyndbg + drm patchset
> has been done using virtme,
> so my world-view (and dev-hack-test env) has been smaller, simpler
> maybe its been fatally simplistic.
> 
> ive just rebuilt v6.0  (before the trouble)
> and run it thru my virtual home box,
> I didnt see any unfamiliar drm-debug output
> that I might have inadvertently altered somehow
> 
> I have some real HW I can put a reference kernel on,0
> to look for the missing output, but its all gonna take some time,
> esp to tighten up my dev-test-env
> 
> in the meantime, there is:
> 
> config DRM_USE_DYNAMIC_DEBUG
> bool "use dynamic debug to implement drm.debug"
> default y
> depends on DRM
> depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
> depends on JUMP_LABEL
> help
>   Use dynamic-debug to avoid drm_debug_enabled() runtime overheads.
>   Due to callsite counts in DRM drivers (~4k in amdgpu) and 56
>   bytes per callsite, the .data costs can be substantial, and
>   are therefore configurable.
> 
> Does changing the default fix things for i915 dmesg ?

I think we want to mark it BROKEN in addition to make sure no one
enables it by accident. We already got one bug report where I had to
ask the reporter to rebuild their kernel since this had gotten
enabled and we didn't get any debugs from the driver probe.

> or is the problem deeper ?
> 
> theres also this Makefile addition, which I might have oversimplified
> 
> CFLAGS-$(CONFIG_DRM_USE_DYNAMIC_DEBUG) += -DDYNAMIC_DEBUG_MODULE

-- 
Ville Syrjälä
Intel