hi all,
Apologies for broad --to, but it touches a wide range, if casually.
In order to avoid runtime costs of drm_debug_enabled(), this patchset re-implements drm.debug to use dyndbg, after extending dyndbg with kernel_param_ops to implement the bitmap->dydnbg-query and expose it for use.
To define your pr_debugs categorization (that you want to control):
DEFINE_DYNDBG_BITMAP(debug_gvt, __gvt_debug, "i915/gvt dyndbg bitmap desc", /* bits 0-N are initialized with these exprs */ { "gvt:cmd: ", "command processing" }, { "gvt:core: ", "core help" }, { "gvt:dpy: ", "display help" }, { "gvt:el: ", "help" }, { "gvt:irq: ", "help" }, { "gvt:mm: ", "help" }, { "gvt:mmio: ", "help" }, { "gvt:render: ", "help" }, { "gvt:sched: ", "help" });
Then, you can change whole categories of pr_debugs:
echo 0x5A > /sys/modules/i915/parameters/debug_gvt
BIT($i++) is implied by order, can it be autogend with macros and stuffed into MODULE_PARAM_DESC automagically ?
v4: - extend kernel_param with void* .data (2/7) - move v3 kernel_param_ops code into dyndbg (3/7) - add DEFINE_DYNDBG_BITMAP (3/7) - use DEFINE_DYNDBG_BITMAP in drm-core, i915 (5/7), amdgpu (7/7) - lots of changes per @DanVet feedback, thanks! no doc yet, content more in commit-log refinements
v3: https://lore.kernel.org/lkml/20210714175138.319514-1-jim.cromie@gmail.com/ main element is now patch 6/7, v2: https://lore.kernel.org/lkml/20210711055003.528167-1-jim.cromie@gmail.com/ v1: https://lore.kernel.org/lkml/20201204035318.332419-1-jim.cromie@gmail.com/
NOTES:
https://github.com/jimc/linux/tree/dd-drm-v4 should be seen and tested by robots soon.
Using dyndbg to implement categories/classes of pr_debugs requires that the class-prefix is compiled into the format string, and not written at runtime with pr_debug("%s %pV", class_str, vaf).
That caveat is reflected in (6/7) where category is catenated with the format, and ceases to exist as a separate arg for DRM_USE_DD=y builds. ISTM this also means drm_debug_enabled() isnt going away just yet.
The categories arent atomic in any sense; callsites controlled via drm.debug can still be tweaked arbitrarily with echo $query > control.
dyndbg's search is global by default; format ^$prefix cuts across code modules, and anyone can add a pr_debug("drm:foobar: yada") classification. Rules against this are policy, and belong in the realm of author taste and code review, not in the tool.
Maybe modname's already available via kp, if we need it. Other query terms are possible, if struct dyndbg_bitdesc is elaborated.
The dyndbg-queries built by the callback don't include modname. This allows drm.dbg to control pr-debugs inside i915, despite being done from a different module. This is ok because i915 used the drm_debug api for those messages.
i915/gvt uses a different way to prepend its classes, but it shares the classification space. Like a good namespace citizen, it has "gvt:" as its top-level name, with ~9 2nd level names.
sean@chromium.org posited "drm:atomic:fail: " as a new category, to leverage the additional selectivity of dyndbg.
Allowing for N-level namespaces, ' ' terminates the prefix, not ':'. So "drm:atomic:" & "drm:atomic: " are different searches, 1st including pr_debug("drm:atomic:fail: ")
DEFINE_DYNDBG_BITMAP() bits and masks are dependent on order of bit-declarations. Since bits are applied 0-N, later bits could override (ie sub-categorize) earlier ones. IOW, "drm:atomic:fail: " just needs to be after "drm:atomic: ".
dyndbg is extremely agnostic about how you use format ^$prefix, your classification scheme just needs to work within the limitation that its a simple anchored literal substring match, no regex stuff.
In particular, commit 578b1e0701af ("dynamic_debug: add wildcard support to filter files/functions/modules") left format out, because it was already special (floating substr match, no need for '*').
Patch 6/7 has many more "advices" on classification / categorization.
and im restating things.
Much more to say/do instead of what follows, which is v3 prose. I wanted to send, see how its received by robots and people.
drm_debug_enabled() is called a lot 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 all those drm_debug_enabled() overheads, if CONFIG_DRM_USE_DYNAMIC_DEBUG=y.
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 running this patchset bare-metal on an i915 laptop & an amdgpu desktop (both as loadable modules). I booted the amdgpu box with:
BOOT_IMAGE=(hd2,gpt2)/vmlinuz-5.13.0-dd7-13692-g8def25788f56 \ 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 3 minutes of tests, causing ~76k prdbgs in 409 seconds, before I turned them off with:
echo module amdgpu -p > /proc/dynamic_debug/control
This is on top of master @ v5.14-rc3.
Jim Cromie (7): drm/print: fixup spelling in a comment (already in drm-mumble) moduleparam: add data member to struct kernel_param dyndbg: add dyndbg-bitmap definer and callbacks i915/gvt: remove spaces in pr_debug "gvt: core:" etc prefixes i915/gvt: control pr_debug("gvt:")s with bits in parameters/debug_gvt drm/print: add choice to use dynamic debug in drm-debug amdgpu: define a dydbg-bitmap to control categorized pr_debugs
drivers/gpu/drm/Kconfig | 13 +++ .../gpu/drm/amd/display/dc/core/dc_debug.c | 42 +++++++- drivers/gpu/drm/drm_print.c | 15 ++- drivers/gpu/drm/i915/gvt/Makefile | 4 + drivers/gpu/drm/i915/gvt/debug.h | 18 ++-- drivers/gpu/drm/i915/i915_params.c | 34 +++++++ include/drm/drm_print.h | 99 ++++++++++++++----- include/linux/dynamic_debug.h | 36 +++++++ include/linux/moduleparam.h | 11 ++- lib/dynamic_debug.c | 55 +++++++++++ 10 files changed, 284 insertions(+), 43 deletions(-)