[PATCH v11 09/19] drm_print: add CONFIG_DRM_USE_DYNAMIC_DEBUG

Jim Cromie
2022-01-07T05:30:13Z

DRM.debug API is used thousands of times in drivers/gpu/drm/*; when
these are implemented using dynamic-debug, DYNAMIC_DEBUG_METADATA adds
a struct _ddebug (56 bytes) per site.

Since i915 will have ~2k callsites, and amdgpu ~4k, the memory costs
are substantial, and thus made configurable.

For a baseline:
bash-5.1# drms_load
[ 10.923093] dyndbg: 1 debug prints in module drm
[ 10.928345] ACPI: bus type drm_connector registered
[ 11.034012] dyndbg: 2 debug prints in module ttm
[ 11.038188] dyndbg: 8 debug prints in module video
[ 11.551064] dyndbg: 127 debug prints in module i915
[ 11.617106] AMD-Vi: AMD IOMMUv2 functionality not available on this system - This is not a bug.
[ 12.084856] dyndbg: 2196 debug prints in module amdgpu
[ 12.099040] [drm] amdgpu kernel modesetting enabled.
[ 12.099790] amdgpu: CRAT table not found
[ 12.100523] amdgpu: Virtual CRAT table created for CPU
[ 12.100901] amdgpu: Topology: Add CPU node
[ 12.165382] dyndbg: 3 debug prints in module wmi
[ 12.356424] dyndbg: 3 debug prints in module nouveau

i915/gvt has pr_debugs that show up here
amdgpu has many pr_debugs from macro expansions

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>

fixup-mk
---
drivers/gpu/drm/Kconfig | 12 ++++++++++++
drivers/gpu/drm/Makefile | 2 ++
2 files changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 0039df26854b..4e7b865c3441 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -62,6 +62,18 @@ config DRM_DEBUG_MM

If in doubt, say "N".

+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.
+
config DRM_DEBUG_SELFTEST
tristate "kselftests for DRM"
depends on DRM
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 0dff40bb863c..60f4d7bc27eb 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -3,6 +3,8 @@
# Makefile for the drm device driver. This driver provides support for the
# Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.

+CFLAGS-$(CONFIG_DRM_USE_DYNAMIC_DEBUG) += -DDYNAMIC_DEBUG_MODULE
+
drm-y := drm_aperture.o drm_auth.o drm_cache.o \
drm_file.o drm_gem.o drm_ioctl.o drm_irq.o \
drm_drv.o \
--
2.33.1