[PATCH v7 0/8] use DYNAMIC_DEBUG to implement DRM.debug

[Jim Cromie]

Hi Jason, DRM folks,

In DRM-debug currently, drm_debug_enabled() is called a lot to decide
whether or not to write debug messages.  Each test is cheap, but costs
continue with uptime.  DYNAMIC_DEBUG "dyndbg", when built with
JUMP_LABEL, replaces each of those tests with a patchable NOOP, for
"zero cost when off" debugs.

this is v7:
- drops RFC distractions -JBaron
- drops patch-1: kp->data addition in moduleparams.h not needed -JBaron
- rework dyndbg callbacks to use kp->arg instead -JBaron
- fixes for problem configs reported -lkp 
- others noted per patch below ---

Broadly, this patchset does 3 things:

Adds DEFINE_DYNAMIC_DEBUG_CATEGORIES, which defines a mapping from
bits to "categorized" pr_debugs, a sysfs interface, and callbacks to
implement the bits as dynamic_debug >controls.  This is modelled after
DRM's debug interface.

Uses the new macro in amdgpu & i915 to control existing pr_debugs
according to their ad-hoc categorizations.

Adapts the drm-debug API (~20 macros) to configurably "replace"
drm_dbg & drm_dev_dbg with pr_debug & dev_dbg, which avoids
drm_debug_enabled() overheads.  DEFINE_DYNAMIC_DEBUG_CATEGORIES is
used to create the controlling bitmap, which is wired to __drm_debug
var so remaining drm_debug_enabled() users stay in sync.

on a virtual box:
bash-5.1# for m in i915 amdgpu nouveau; do modprobe $m; done
[43833.332326] dyndbg: 384 debug prints in module drm
[43833.609577] dyndbg: 211 debug prints in module drm_kms_helper
[43833.707124] dyndbg:   2 debug prints in module ttm
[43837.471166] dyndbg: 1727 debug prints in module i915
[43838.030774] AMD-Vi: AMD IOMMUv2 driver by Joerg Roedel <jroedel@xxxxxxx>
[43838.031905] AMD-Vi: AMD IOMMUv2 functionality not available on this system
[43846.209583] dyndbg: 3852 debug prints in module amdgpu
[43846.261391] [drm] amdgpu kernel modesetting enabled.
[43846.262512] amdgpu: CRAT table not found
[43846.263264] amdgpu: Virtual CRAT table created for CPU
[43846.264293] amdgpu: Topology: Add CPU node
[43846.743781] dyndbg:   3 debug prints in module wmi
[43852.517497] dyndbg:  92 debug prints in module nouveau

There are a few multi-second delays there, just before dyndbg
initializes the large blocks of debug prints.


Jim Cromie (8):
  dyndbg: add DEFINE_DYNAMIC_DEBUG_CATEGORIES and callbacks
  dyndbg: remove spaces in pr_debug "gvt: core:" etc prefixes
  i915/gvt: use DEFINE_DYNAMIC_DEBUG_CATEGORIES to create "gvt:core:"
    etc categories
  amdgpu: use DEFINE_DYNAMIC_DEBUG_CATEGORIES
  drm_print: add choice to use dynamic debug in drm-debug
  drm_print: instrument drm_debug_enabled
  amdgpu_ucode: reduce number of pr_debug calls
  nouveau: fold multiple DRM_DEBUG_DRIVERs together

 drivers/gpu/drm/Kconfig                       |  13 +
 drivers/gpu/drm/Makefile                      |   3 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_ucode.c     | 293 ++++++++++--------
 .../gpu/drm/amd/display/dc/core/dc_debug.c    |  44 ++-
 drivers/gpu/drm/drm_print.c                   |  53 +++-
 drivers/gpu/drm/i915/Makefile                 |   4 +
 drivers/gpu/drm/i915/gvt/debug.h              |  18 +-
 drivers/gpu/drm/i915/i915_params.c            |  35 +++
 drivers/gpu/drm/nouveau/nouveau_drm.c         |  36 ++-
 include/drm/drm_print.h                       | 150 +++++++--
 include/linux/dynamic_debug.h                 |  60 ++++
 lib/dynamic_debug.c                           |  79 ++++-
 12 files changed, 582 insertions(+), 206 deletions(-)

-- 
2.31.1