New subject: [PATCH v2 01/27] dyndbg: fix static_branch manipulation

16 May 2022


      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.
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?
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.
- api use needs review wrt drm life-cycle.
  enum drm_debug_category and DYNAMIC_DEBUG_CLASSES could be together?
- class-names could stand review, perhaps extension
  "drm:core:" etc have appeared (maybe just from me)
  or a "plan" to look at it later
- 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.
- 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");
- nouveau has very few drm.debug calls,
  has NV_DEBUG, VMM_DEBUG, nvkm_printk_, I havent looked deeply.
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....
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 Syrjälä 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

[RFC PATCH v2 00/27] DRM.debug on DYNAMIC_DEBUG, add trace events