Hi Jason, Greg, Daniel, 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.
Broadly, this patchset does 3 things, in 2 trees:
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. CONFIG_DRM_USE_DYNAMIC_DEBUG controls this; the memory costs are substantial (many new/converted drm callsites, 56 bytes/pr_debug), so the choice should be made by the user.
#prdbgs KiB #with DRM_USE_DYNAMIC_DEBUG=y kernel 3079 166k drm 1 .06k 376 21k drm_kms_helper 207 12k i915 167 9.3k 1811 101k amdgpu 2339 130k 3917 220k nouveau 3 .17k 105 ~60k
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.
this is v8: - 7 small tweaks to dyndbg pr-infos etc, no functional changes - drop help field from dyndbg_bitdesc - simplify declarative interface - move ^ anchor, trailing space to macro helper this makes callback slightly more generic - i915/gvt move code, Makefile bits per Tvrtko - mem cost numbers - more CI fixes
I think the dyndbg patches qualify to get in this cycle; all but the last are no-functional-changes, the last is a new feature (which uses existing mechanics without any adjustments), and has no users yet, so it can't cause regressions.
Obviously, DRM is the anticipated user. I've fixed the patchwork CI problems I have seen on v6, v7, and lkp-robot reports since. Since CONFIG_DRM_USE_DYNAMIC_DEBUG=y by default, it should have seen "on" testing, not just "off" testing.
Jim Cromie (16):
Dyndbg no-functional-changes chunk: dyndbg: add module to a vpr-info in dd-exec-queries dyndbg: pr-info in boot-param should say so dyndbg: rationalize verbosity dyndbg: use alt-quotes in vpr-infos, not those user might use dyndbg: vpr-info on remove-module complete, not starting dyndbg: no vpr-info on empty queries dyndbg-doc: fix bootparam usage example (possible conflict
New Feature, using unchanged mechanisms: dyndbg: add DEFINE_DYNAMIC_DEBUG_CATEGORIES bitmap and callbacks
DRM 1st user(s): drm: fix doc grammar error i915/gvt: remove spaces in pr_debug "gvt: core:" etc prefixes i915/gvt: use DEFINE_DYNAMIC_DEBUG_CATEGORIES for existing prdbgs amdgpu: use DEFINE_DYNAMIC_DEBUG_CATEGORIES on existing prdbgs 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
.../admin-guide/dynamic-debug-howto.rst | 8 +- drivers/gpu/drm/Kconfig | 26 ++ drivers/gpu/drm/Makefile | 3 + drivers/gpu/drm/amd/amdgpu/Makefile | 2 + drivers/gpu/drm/amd/amdgpu/amdgpu_ucode.c | 293 ++++++++++-------- .../gpu/drm/amd/display/dc/core/dc_debug.c | 43 ++- drivers/gpu/drm/drm_print.c | 53 +++- drivers/gpu/drm/i915/Makefile | 2 + drivers/gpu/drm/i915/gvt/debug.h | 18 +- drivers/gpu/drm/i915/intel_gvt.c | 34 ++ drivers/gpu/drm/nouveau/nouveau_drm.c | 36 ++- include/drm/drm_drv.h | 2 +- include/drm/drm_print.h | 184 ++++++++--- include/linux/dynamic_debug.h | 62 ++++ lib/dynamic_debug.c | 121 ++++++-- 15 files changed, 650 insertions(+), 237 deletions(-)