[PATCH v5 0/9] dyndbg: add DEFINE_DYNAMIC_DEBUG_CATEGORIES and use in DRM

From: Jim Cromie
Date: Fri Aug 13 2021 - 11:23:37 EST


hi Jason, Greg, Daniel, dri-everyone,

drm_debug_enabled() is called a lot (by drm-debug api) to do unlikely
bit-tests to selectively enable debug printing; this is a good job for
DYNAMIC_DEBUG, IFF it is built with JUMP_LABEL.

This patchset enables the use of dynamic-debug to avoid those
drm_debug_enabled() overheads, if CONFIG_DRM_USE_DYNAMIC_DEBUG=y.

v5: much rework

- based on Daniel Vetter's feedback, not RFC anymore. (except last one)

- move POC bit_map callback code into dynamic_debug
add .data to struct kernel_param
add DEFINE_DYNAMIC_DEBUG_CATEGORIES :
a declarative interface for bits => control-queries
this is all new functionality.

- use DEFINE_DYNAMIC_DEBUG_CATEGORIES in i915, amdgpu
adds selectivity/control to existing categorizations

- DRM_USE_DYNAMIC_DEBUG
replace DRM_UT_<CAT> (an enum)
with DRM_CAT_<CAT> (a prefix string, cpp-prepended to format)
_UT_ still present, drm_debug_enabled() still used
todo:
change __drm_debug param-var to read DDD_CATEGORIES's param-var
might suffice to keep parallel schemes coherent.

- RFC add tracer func as syslog alternate
test_dynamic_debug.ko: uses tracer for observability, does selftest
has some misuse risk; calling pr_debug recursively.

v4: (brown-bagger, various fixes after snips)
v3: fixes missed SOB, && on BOL, commit-log tweaks
v2: https://lore.kernel.org/lkml/20210711055003.528167-1-jim.cromie@xxxxxxxxx/
v1: https://lore.kernel.org/lkml/20201204035318.332419-1-jim.cromie@xxxxxxxxx/

Doing so creates many new pr_debug callsites,
otherwise i915 has ~120 prdbgs, and drm has just 1;

bash-5.1# modprobe i915
dyndbg: 8 debug prints in module video
dyndbg: 305 debug prints in module drm
dyndbg: 207 debug prints in module drm_kms_helper
dyndbg: 2 debug prints in module ttm
dyndbg: 1720 debug prints in module i915

On amdgpu, enabling it adds ~3200 prdbgs, currently at 56 bytes each.
So CONFIG_DRM_USE_DYNAMIC_DEBUG=y affects resource requirements.
Im working on a diet-plan.

Im running this patchset bare-metal on an i7/i915 laptop & an
r9/amdgpu desktop (both as loadable modules). I booted the amdgpu box
with:

BOOT_IMAGE=(hd2,gpt2)/vmlinuz-5.14.0-rc4-d7a-00009-g5db471cba844 \
root=UUID=mumble ro \
rootflags=subvol=root00 rhgb \
dynamic_debug.verbose=3 main.dyndbg=+p \
amdgpu.debug=1 amdgpu.test=1 \
"amdgpu.dyndbg=format ^[ +p"

That last line enables ~1700 prdbg callsites with a format like '[DML'
etc at boot, and amdgpu.test=1 triggers 90 seconds of tests, yielding
~76k prdbgs in 409 seconds, before I turned them off with:

echo module amdgpu -p > /proc/dynamic_debug/control

Its worth noting, this changes the dyndbg-state underneath settings
applied with `echo > parameters/debug`; the latter is qualitatively
writeonly, maybe a param_get should return "NA" "-1"

this merged cleanly, on top of
commit d65ef4634e5c795a6a4df1d198992c70e9692fb3 (drm-tip/drm-tip)

Jim Cromie (9):
drm/print: fixup spelling in a comment
moduleparam: add data member to struct kernel_param
dyndbg: add DEFINE_DYNAMIC_DEBUG_CATEGORIES and callbacks
i915/gvt: 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 to control categorized
pr_debugs
drm_print: add choice to use dynamic debug in drm-debug
amdgpu_ucode: reduce number of pr_debug calls
dyndbg: RFC add tracer facility RFC

drivers/gpu/drm/Kconfig | 13 +
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 | 49 ++-
drivers/gpu/drm/i915/gvt/Makefile | 4 +
drivers/gpu/drm/i915/gvt/debug.h | 18 +-
drivers/gpu/drm/i915/i915_params.c | 35 +++
include/drm/drm_print.h | 143 +++++++--
include/linux/dynamic_debug.h | 82 ++++-
include/linux/moduleparam.h | 11 +-
lib/Kconfig.debug | 10 +
lib/Makefile | 1 +
lib/dynamic_debug.c | 171 ++++++++--
lib/test_dynamic_debug.c | 247 +++++++++++++++
14 files changed, 901 insertions(+), 220 deletions(-)
create mode 100644 lib/test_dynamic_debug.c

--
2.31.1