[PATCH v4] drm/trace: Buffer DRM logs in a ringbuffer accessible via debugfs

[Steven Rostedt]

On Tue, 14 Jan 2020 12:21:43 -0500
Sean Paul <sean at poorly.run> wrote:

> From: Sean Paul <seanpaul at chromium.org>
> 
> 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.

You may want to rebase these on my tree that renames ring_buffer to
trace_buffer. For more information, read this thread:

  https://lore.kernel.org/r/20191213153553.GE20583@krava

My tree is currently being tested and when it finishes contingent on no
errors found, I'll be pushing it to linux-next.

 https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git/commit/?h=ftrace/core&id=13292494379f92f532de71b31a54018336adc589

-- Steve


> 
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: David Airlie <airlied at gmail.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Pekka Paalanen <ppaalanen at gmail.com>
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: Steven Rostedt <rostedt at goodmis.org>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Sean Paul <seanpaul at chromium.org>
> Link: https://patchwork.freedesktop.org/patch/msgid/20191010204823.195540-1-sean@poorly.run #v1
> Link: https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html #v2
> Link: https://patchwork.freedesktop.org/patch/msgid/20191212203301.142437-1-sean@poorly.run #v3
> 
> Changes in v2:
> - Went with a completely different approach:
> https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html
> 
> Changes in v3:
> - Changed commit message to be a bit less RFC-y
> - Make class_drm_category_log an actual trace class
> 
> Changes in v4:
> - Instead of [ab]using trace events and the system trace buffer, use our
>   own ringbuffer
> ---