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Date:   Wed, 25 May 2022 17:02:44 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Jim Cromie <jim.cromie@gmail.com>
Cc:     jbaron@akamai.com, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
        intel-gvt-dev@lists.freedesktop.org,
        intel-gfx@lists.freedesktop.org, gregkh@linuxfoundation.org,
        daniel.vetter@ffwll.ch, seanpaul@chromium.org, robdclark@gmail.com,
        rostedt@goodmis.org, mathieu.desnoyers@efficios.com,
        quic_saipraka@quicinc.com, will@kernel.org,
        catalin.marinas@arm.com, quic_psodagud@quicinc.com, maz@kernel.org,
        arnd@arndb.de, linux-arm-kernel@lists.infradead.org,
        linux-arm-msm@vger.kernel.org, mingo@redhat.com,
        David Airlie <airlied@gmail.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Pekka Paalanen <ppaalanen@gmail.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Ville =?iso-8859-1?Q?Syrj=E4l=E4?= 
        <ville.syrjala@linux.intel.com>,
        Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [RFC PATCH v2 00/27] DRM.debug on DYNAMIC_DEBUG, add trace events
Message-ID: <Yo5FFMbNG1Viirj1@phenom.ffwll.local>
Mail-Followup-To: Jim Cromie <jim.cromie@gmail.com>, jbaron@akamai.com,
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        intel-gfx@lists.freedesktop.org, gregkh@linuxfoundation.org,
        seanpaul@chromium.org, robdclark@gmail.com, rostedt@goodmis.org,
        mathieu.desnoyers@efficios.com, quic_saipraka@quicinc.com,
        will@kernel.org, catalin.marinas@arm.com, quic_psodagud@quicinc.com,
        maz@kernel.org, arnd@arndb.de, linux-arm-kernel@lists.infradead.org,
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        David Airlie <airlied@gmail.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Pekka Paalanen <ppaalanen@gmail.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Ville =?iso-8859-1?Q?Syrj=E4l=E4?= <ville.syrjala@linux.intel.com>,
        Chris Wilson <chris@chris-wilson.co.uk>
References: <20220516225640.3102269-1-jim.cromie@gmail.com>
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On Mon, May 16, 2022 at 04:56:13PM -0600, Jim Cromie wrote:
> DRM.debug API is 23 macros, issuing 10 exclusive categories of debug
> messages.  By rough count, they are used 5140 times in the kernel.
> These all call drm_dbg or drm_devdbg, which call drm_debug_enabled(),
> which checks bits in global __drm_debug.  Some of these are page-flips
> and vblanks, and get called often.
> 
> DYNAMIC_DEBUG (with CONFIG_JUMP_LABEL) is built to avoid this kind of
> work, with NOOPd jump/callsites.
> 
> This patchset is RFC because:
> - it touches 2.5 subsystems: dyndbg, drm, tracefs (new events)
> - dyndbg class support is built for drm, needs it for validation
> - new api, used by drm
> - big memory impact, with 5100 new pr-debug callsites.
> - drm class bikeshedding opportunities
> - others, names etc.

Thanks a lot for keeping on pushing this!

> 
> DYNAMIC_DEBUG:
> 
> Adapt to directly represent 32 exclusive classes / categories.
> All existing users get _CLASS_DFLT:31, reserving 0-30 for opt-in.
> 
> dynamic_debug_register_classes(): Tells dyndbg that caller/client is
> using .class_id's 0..N, and wants them exposed and manipulatable with
> names: DRM_UT_KMS etc.
> 
> Client invokes DYNAMIC_DEBUG_CLASSES to define the name->id map,
> then registers it during its initialization.
> 
> Then, when a dyndbg command-query has "class FOO":
> 
>  echo class DRM_UT_KMS +p > /proc/dynamic_debug/control
> 
> ddebug_change() will 1st ddebug_validate_classname() for each module,
> using its registered class-maps; only modules which know DRM_UT_KMS
> will get those callsite adjustments.  This "protects" each module's
> class-id space, unlike "class 4" query syntax.
> 
> Add bitmap support for:
>   echo 0x02 > /sys/module/drm/parameters/debug
> 
> Add symbolic bitmap, because we have the class-names:
>   echo +DRM_UT_KMS,+DRM_UT_ATOMIC > /sys/module/drm/parameters/debug
> 
> Add test_dynamic_debug, to prove out the API.
> 
>  which is (used 3x to prove class-id ranges):
>   - DYNAMIC_DEBUG_CLASSES(var, ... [3 class-name-literals each])
>   - dynamic_debug_register_classes(var)
>   - dynamic_debug_unregister_classes(var)
>  also (6x):
>   +module_param_cb(<node-name>, &param_ops_dyndbg_classes, /[pt][123]_bitmap/, 0600);
> 
> Bits 0,1,2 of each of the 6 bitmaps control the 3 named classes in
> each of 3 groups, toggling their p,T bits respectively.
> 
> RFC:
> 
> dynamic_debug_register_classes() cannot act early enough to be in
> effect at module-load.  So this will not work as you'd reasonably
> expect:
> 
>   modprobe test_dynamic_debug dyndbg='+pfm; class FOO +pfmlt'
> 
> The 1st query:+pfm will be enabled during load, but in the 2nd query,
> "class FOO" will be unknown at load time.  Early class enablement
> would be nice.  DYNAMIC_DEBUG_CLASSES is a static initializer, which
> is certainly early enough, but Im missing a trick, suggestions?

So maybe I'm just totally overloading this work here so feel free to
ignore or postpone, but: Could we do the dynamic_debug_register_classes()
automatically at module load as a new special section? And then throw in a
bit of kbuild so that in a given subsystem every driver gets the same
class names by default and everything would just work, without having to
sprinkle calls to dynamic_debug_register_classes() all over the place?
That kbuild magic could then also insert all the boilerplate to make the
module options work, or maybe you could push that all into the module
loader and it would add these special options on its own (yay for more
consistency across subsystems)?

Also I think with that the early class stuff should be possible to fix,
since you can make sure that the classes are all there (in the module
loader code) before anything else gets done. A bit a special case but oh
well.
 
For the entire class approach, did you spot another subsystem that could
benefit from this and maybe make a more solid case that this is something
good?

> Wildcarding on classname is possible, maybe useful:
> 
>    echo +DRM_UT_\* > /sys/module/drm/parameters/debug
> 
> If contemplated in earnest, it should consider the difference between
> "DRM_*" and "*_KMS", wrt observing across class hierarchies, as well
> as decide whether that echo means 1st match, or all matching names.
> 
> __pr_debug_cls(cls, fmt,...) is just for testing, drm doesnt need it.
> 
> 
> DRM adaptation:
> 
> Basically, these patches add another layer of macro indirection, which
> by CONFIG_DRM_USE_DYNAMIC_DEBUG=y, wraps drm_*dbg() in dyndbg's callsite
> Factory macro, and adds the new descriptor arg to the funcs.
> 
> With these patches, drm.debugs appear as controllable *pr-dbg* callsites:
> 
> [   11.804352] dyndbg: register_classes: drm
> [   11.920715] dyndbg: 234 debug prints in module drm_kms_helper
> [   11.932135] dyndbg:   2 debug prints in module ttm
> [   11.936119] dyndbg:   8 debug prints in module video
> [   12.537543] dyndbg: 1756 debug prints in module i915
> [   12.555045] dyndbg: register_classes: i915
> [   12.666727] AMD-Vi: AMD IOMMUv2 functionality not available on this ..
> [   13.735310] dyndbg: 3859 debug prints in module amdgpu
> 
> amdgpu's large count includes:
>    582  direct uses/mentions of pr_debug
>     43  defns of DC_LOG_*, which use either pr_debug or DRM_DEBUG_*
>  ~1000  uses of DC_LOG_*
>   1116  uses of dml_print in drivers/gpu/drm/amd
>     15  drm_dbg_\\w+ drivers/gpu/drm/amd
>    273  DRM_DEBUG_\\w+ drivers/gpu/drm/amd    
> 
> i915 has:
>   1072  drm_dbg_\\w+ drivers/gpu/drm/i915/ | wc  -l
>    200  DRM_DEBUG_\\w+ drivers/gpu/drm/i915/
>     46  pr_debug drivers/gpu/drm/i915/
>    144  gvt_dbg_\\w+ drivers/gpu/drm/i915/gvt, using pr_debug
> 
> This impacts the data footprint, so everything new/drm is dependent on
> DRM_USE_DYNAMIC_DEBUG=y.
> 
> RFC for DRM:
> 
> - decoration flags "fmlt" do not work on drm_*dbg().
>   (drm_*dbg() dont use pr_debug, they *become* one flavor of them)
>   this could (should?) be added, and maybe tailored for drm.
>   some of the device prefixes are very long, a "d" flag could optionalize them.

I'm lost what the fmlt decoration flags are?

> - api use needs review wrt drm life-cycle.
>   enum drm_debug_category and DYNAMIC_DEBUG_CLASSES could be together?

Hm if they're tied to module lifetime we should be good? Not sure what
could go wrong here.

> - class-names could stand review, perhaps extension
>   "drm:core:" etc have appeared (maybe just from me)
>   or a "plan" to look at it later

Yeah it's been a bit sprawling. I'm kinda hoping that by firmly
establishing dyndbg as the drm debug approach we can cut down for the need
for ad-hoc flags a bit.

> - i915 & amdgpu have pr_debugs (DC_LOG_*, gvt_dbg_*) that have
> class-ish prefixes that are separate from, but similar to DRM_UT_*,
> and could stand review and possible unification with reformed or
> extended drm categories.

Yeah drm is not entirely consistent with how exactly driver debug printing
should be done. Another reason why I'm hoping that the kitchen sync with
everything approach you're doing here could help unify things.

> - the change to enum drm_debug_category from bitmask values to 0..31
>   means that we foreclose this possiblility:
> 
>    drm_dbg(DRM_UT_CORE|DRM_UT_KMS, "wierd double-cat experiment");

Yeah no, that doesn't make much sense to me :-)

> - nouveau has very few drm.debug calls,
>   has NV_DEBUG, VMM_DEBUG, nvkm_printk_, I havent looked deeply.

Yeah see above. There's a pile more drivers (more on the armsoc side of
things) which are quite big on the raw debug call approach.

Cheers, Daniel

> 
> DYNDBG/DRM -> TRACEFS
> 
> My 1st try was motivated by Sean Paul's patch - DRM.trace:
> https://patchwork.freedesktop.org/patch/445549/?series=78133&rev=5
> 
> Those used trace_printk, so were not good for upstream.
> 
> Vincent Whitchurch's code:
> https://lore.kernel.org/lkml/20200721141105.16034-1-vincent.whitchurch@axis.com/
> 
> added similar features, by sending printk:console events from dyndbg.
> It met with a good reception from Steve Rostedt, so I re-started with
> that.
> 
> The biggest addition (from UI viewpoint) is 4 new trace-events, 2 each
> from dyndbg (pr_debug, dev_dbg) and drm (drm_dbg, drm_dev_dbg); 2 have
> dev, other 2 avoid storing nulls.  Im unsure that 4 distinctions is
> valuable, but it seemed most obvious to reflect them straight thru to
> tracefs.
> 
> RFC: the event/message formats are a bit of a mash-up; 
> 
> in /sys/kernel/tracing:
> drm/drm_debug/format:print fmt: "%s", __get_str(msg)
> drm/drm_devdbg/format:print fmt: "cat:%d, %s %s", \
> 	REC->drm_debug_category, dev_name(REC->dev), __get_str(msg)
> 
> The 1st prints just the mesg itself, 2nd prints category as int;
> it'd be better if DRM.class-name replaced (not just augmented) the
> event-name "drm_devdbg" in the trace, is that possible ?
> 
> dyndbg/prdbg/format:
> print fmt: "%s.%s %s", REC->desc->modname, REC->desc->function, __get_str(msg)
> dyndbg/devdbg/format:
> print fmt: "%s.%s %s", REC->desc->modname, REC->desc->function, __get_str(msg)
> 
> These add a prefix string similar to dyndbg's decorations, except they
> don't use dyndbg's "fmlt" decoration flags.
> 
> There are also 3 vblank trace-events already,
>   declared in: drivers/gpu/drm/drm_trace.h
> 15:TRACE_EVENT(drm_vblank_event,
> 35:TRACE_EVENT(drm_vblank_event_queued,
> 52:TRACE_EVENT(drm_vblank_event_delivered,
> 
> STATUS
> 
> kernel-test-robot tested this patchset (on 5.18-rc6).
> github:[jimc:blead] BUILD SUCCESS 6c59e52ac81dd81ac7da4522a5e15b7ac488d5b5
> May 15, 2022, 8:39 AM (1 day ago)
> 
> 
> Ive been testing, mostly on virtme, mostly with this:
> #!/bin/bash
> 
> # test class FOO handling of dynamic-debug
> 
> alias lmt='modprobe test_dynamic_debug dyndbg=+pmf'
> alias rmt='rmmod test_dynamic_debug'
> alias look='grep test_dynamic_debug /proc/dynamic_debug/control'
> 
> lookfor() {
>     grep $1 /proc/dynamic_debug/control
> }
> 
> vx() {
>     echo $* > /sys/module/dynamic_debug/parameters/verbose
> }
> 
> # amdgpu has ~2200 pr-debugs (before drm-debug-on-dyndbg),
> # use them to prove modprobe <mod> dyndbg=+p works
> 
> test_param_dyndbg() {
> 
>     modprobe amdgpu dyndbg=+pfm
>     let count=$(grep =pmf /proc/dynamic_debug/control | grep amdgpu | wc -l)
> 
>     if [ $count -gt 200 ] ; then
> 	echo amdgpu has $count pr-dbgs
> 	return 0
>     else
> 	echo failed $count
> 	return -1
>     fi
> }
> out=$(test_param_dyndbg)
> echo out:$out $?
> [ $? -eq 0 ] || exit $?
> 
> qry_cmd() {
>     echo "QCMD: $*   >control" >&2
>     echo $* > /proc/dynamic_debug/control
> }
> 
> # enable dyndbg tracing
> dynable() {
>     grep -P \\d $SKT/events/dyndbg/{.,*}/enable
>     echo 1 > $SKT/events/dyndbg/enable
>     grep -P \\d $SKT/events/dyndbg/{.,*}/enable
> }
> 
> # enable drm tracing
> drmable() {
>     grep -P \\d $SKT/events/drm/{.,*}/enable
>     echo 1 > $SKT/events/drm/enable
>     grep -P \\d $SKT/events/drm/{.,*}/enable
> }
> 
> function doit() {
>     cat /sys/module/test_dynamic_debug/parameters/do_prints
> }
> 
> # test class FOO behavior of test_dynamic_debug module
> ttest_module__() {
>     flg=$1
>     dmesg -C
>     modprobe test_dynamic_debug dyndbg=+pfm
>     doit
> 
>     for cls in FOO BAR BUZZ; do
> 	qry_cmd module test_dynamic_debug class $cls $flg
> 	doit
>     done
>     doit
> 
>     for cls in Foo Bar Buzz; do
> 	qry_cmd module test_dynamic_debug class $cls $flg
> 	doit
>     done
>     doit
> 
>     for cls in bing bong boom; do
> 	qry_cmd module test_dynamic_debug class $cls $flg
> 	doit
>     done
>     doit
> 
>     dmesg | grep class
> }
> 
> ttest_module() {
> 
>     ttest_module__ +p
>     ttest_module__ -p
> 
>     #ttest_module__ +T
>     #ttest_module__ -T
> }
> 
> #dynable
> #drmable
> 
> ttest_module
> grep test_dyn /proc/dynamic_debug/control
> 
> 
> # use/test bitmaps
> 
> set_tddm_() {
>     val=$1;
>     knob=$2;
>     echo "TDDM: $val >$knob" >&2
>     echo $val > /sys/module/test_dynamic_debug/parameters/$knob
>     cat /sys/module/test_dynamic_debug/parameters/$knob
> }
> 
> CLS_1="FOO -FOO +FOO -FOO BAR -BAR +BAR -BAR BUZZ -BUZZ +BUZZ -BUZZ"
> CLS_2=" Foo  Bar  Buzz -Foo -Bar -Buzz +Foo +Bar +Buzz -Foo -Bar -Buzz"
> CLS_3=" bing bong boom -bing -bong -boom +bing +bong +boom -bing -bong -boom"
> 
> tddm_sysnode_classes__() {
>     targ=$1
>     shift
>     cls=$*
>     for bitsym in $cls;
>     do
> 	set_tddm_ $bitsym $targ
>     done
> }
> 
> # work all 3 sysfs bitmaps
> 
> for sysnode in c1_syslog_bits c2_syslog_bits c3_syslog_bits;
> do
>     for val in 0 1 2 4 8 0;
>     do
> 	tddm_sysnode_classes__ $sysnode $val
>     done
> done
> 
> tddm_sysnode_classes__ c1_syslog_bits $CLS_1
> tddm_sysnode_classes__ c2_syslog_bits $CLS_2
> tddm_sysnode_classes__ c3_syslog_bits $CLS_3
> 
> echo "show unknown: c3-names on c1-knob" >&2
> tddm_sysnode_classes__ c1_trace_bits $CLS_3
> 
> echo "flags look inverted" >&2
> tddm_sysnode_classes__ c1_syslog_bits $CLS_1
> 
> CLS_1_=FOO,-FOO,+FOO,-FOO,BAR,-BAR,+BAR,-BAR,BUZZ,-BUZZ,+BUZZ,-BUZZ
> CLS_2_=Foo,Bar,Buzz,-Foo,-Bar,-Buzz,+Foo,+Bar,+Buzz,-Foo,-Bar,-Buzz
> # leading err doesnt wreck the rest
> CLS_3_=,bing,bong,boom,-bing,-bong,-boom,+bing,+bong,+boom,-bing,-bong,-boom
> 
> tddm_sysnode_classes__ c1_syslog_bits $CLS_1_
> tddm_sysnode_classes__ c2_syslog_bits $CLS_2_
> tddm_sysnode_classes__ c3_syslog_bits $CLS_3_
> 
> 
> Cc: Sean Paul <seanpaul@chromium.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Pekka Paalanen <ppaalanen@gmail.com>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Ville Syrj?l? <ville.syrjala@linux.intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> 
> Jim Cromie (27):
>   dyndbg: fix static_branch manipulation
>   dyndbg: show both old and new in change-info
>   dyndbg: fix module.dyndbg handling
>   dyndbg: drop EXPORTed dynamic_debug_exec_queries
>   dyndbg: add exclusive class_id to pr_debug callsites
>   dyndbg: add dynamic_debug_(un)register_classes
>   dyndbg: validate class FOO on module
>   dyndbg: add drm.debug style bitmap support
>   Doc/dyndbg: document new class class_name query support
>   dyndbg: let query-modname override defaulting modname
>   dyndbg: support symbolic class-names in bitmap
>   dyndbg: change zero-or-one classes-map to maps list
>   dyndbg: add __pr_debug_cls(class, fmt, ...)
>   dyndbg: add test_dynamic_debug module
>   drm: POC drm on dyndbg - map class-names to drm_debug_category's
>   drm/print: POC drm on dyndbg - use bitmap
>   drm_print: condense enum drm_debug_category
>   drm_print: interpose drm_*dbg with forwarding macros
>   drm_print: wrap drm_*_dbg in dyndbg descriptor factory macro
>   drm_print: refine drm_debug_enabled for jump-label
>   drm_print: prefer bare printk KERN_DEBUG on generic fn
>   drm_print: add _ddebug desc to drm_*dbg prototypes
>   dyndbg: add _DPRINTK_FLAGS_ENABLED
>   dyndbg: add _DPRINTK_FLAGS_TRACE
>   dyndbg: add write-events-to-tracefs code
>   dyndbg: 4 new trace-events: pr_debug, dev_dbg, drm_{,dev}debug
>   dyndbg/drm: POC add tracebits sysfs-knob
> 
>  .../admin-guide/dynamic-debug-howto.rst       |  12 +
>  MAINTAINERS                                   |   1 +
>  drivers/gpu/drm/Kconfig                       |  12 +
>  drivers/gpu/drm/Makefile                      |   2 +
>  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c       |   3 +
>  drivers/gpu/drm/drm_drv.c                     |   5 +
>  drivers/gpu/drm/drm_print.c                   |  69 ++-
>  drivers/gpu/drm/i915/i915_module.c            |  11 +
>  drivers/gpu/drm/nouveau/nouveau_drm.c         |   4 +
>  include/drm/drm_drv.h                         |  26 +
>  include/drm/drm_print.h                       |  84 ++-
>  include/linux/dynamic_debug.h                 | 136 ++++-
>  include/trace/events/drm.h                    |  68 +++
>  include/trace/events/dyndbg.h                 |  74 +++
>  lib/Kconfig.debug                             |  11 +
>  lib/Makefile                                  |   1 +
>  lib/dynamic_debug.c                           | 487 +++++++++++++++---
>  lib/test_dynamic_debug.c                      | 172 +++++++
>  18 files changed, 1049 insertions(+), 129 deletions(-)
>  create mode 100644 include/trace/events/drm.h
>  create mode 100644 include/trace/events/dyndbg.h
>  create mode 100644 lib/test_dynamic_debug.c
> 
> -- 
> 2.35.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch