1 .. SPDX-License-Identifier: GPL-2.0
2 .. include:: <isonum.txt>
3
4 ==============================================
5 ``amd-pstate`` CPU Performance Scaling Driver
6 ==============================================
7
8 :Copyright: |copy| 2021 Advanced Micro Devices
9
10 :Author: Huang Rui <ray.huang@amd.com>
11
12
13 Introduction
14 ===================
15
16 ``amd-pstate`` is the AMD CPU performance scal
17 new CPU frequency control mechanism on modern
18 Linux kernel. The new mechanism is based on Co
19 Performance Control (CPPC) which provides fine
20 than legacy ACPI hardware P-States. Current AM
21 the ACPI P-states driver to manage CPU frequen
22 only in 3 P-states. CPPC replaces the ACPI P-s
23 flexible, low-latency interface for the Linux
24 communicate the performance hints to hardware.
25
26 ``amd-pstate`` leverages the Linux kernel gove
27 ``ondemand``, etc. to manage the performance h
28 CPPC hardware functionality that internally fo
29 specification (for details refer to AMD64 Arch
30 Volume 2: System Programming [1]_). Currently,
31 frequency control function according to kernel
32 Zen2 and Zen3 processors, and we will implemen
33 in future after we verify them on the hardware
34
35
36 AMD CPPC Overview
37 =======================
38
39 Collaborative Processor Performance Control (C
40 continuous, abstract, and unit-less performanc
41 not tied to a specific performance state / fre
42 standard [2]_ which software can specify appli
43 hints as a relative target to the infrastructu
44 provide the low latency register model (MSR) i
45 interpreter for performance adjustments. ``amd
46 ``struct cpufreq_driver`` instance, ``amd_psta
47 to manage each performance update behavior. ::
48
49 Highest Perf ------>+-----------------------+
50 | |
51 | |
52 | |
53 | |
54 | |
55 Nominal Perf ------>+-----------------------+
56 | |
57 | |
58 | |
59 | |
60 | |
61 | |
62 | |
63 | |
64 | |
65 | |
66 | |
67 | |
68 | |
69 | |
70 | |
71 | |
72 Lowest non- | |
73 linear perf ------>+-----------------------+
74 | |
75 | |
76 | |
77 Lowest perf ------>+-----------------------+
78 | |
79 | |
80 | |
81 0 ------>+-----------------------+
82
83 AMD P-Sta
84
85
86 .. _perf_cap:
87
88 AMD CPPC Performance Capability
89 --------------------------------
90
91 Highest Performance (RO)
92 .........................
93
94 This is the absolute maximum performance an in
95 assuming ideal conditions. This performance le
96 for long durations and may only be achievable
97 are in a specific state; for example, it may r
98 an idle state. This would be equivalent to the
99 supported by the processor.
100
101 Nominal (Guaranteed) Performance (RO)
102 ......................................
103
104 This is the maximum sustained performance leve
105 ideal operating conditions. In the absence of
106 thermal, etc.), this is the performance level
107 be able to maintain continuously. All cores/pr
108 able to sustain their nominal performance stat
109
110 Lowest non-linear Performance (RO)
111 ...................................
112
113 This is the lowest performance level at which
114 achieved, for example, due to the combined eff
115 scaling. Above this threshold, lower performan
116 more energy efficient than higher performance
117 effectively conveys the most efficient perform
118
119 Lowest Performance (RO)
120 ........................
121
122 This is the absolute lowest performance level
123 performance level lower than the lowest nonlin
124 cause an efficiency penalty but should reduce
125 consumption of the processor.
126
127 AMD CPPC Performance Control
128 ------------------------------
129
130 ``amd-pstate`` passes performance goals throug
131 register drives the behavior of the desired pe
132
133 Minimum requested performance (RW)
134 ...................................
135
136 ``amd-pstate`` specifies the minimum allowed p
137
138 Maximum requested performance (RW)
139 ...................................
140
141 ``amd-pstate`` specifies a limit the maximum p
142 to be supplied by the hardware.
143
144 Desired performance target (RW)
145 ...................................
146
147 ``amd-pstate`` specifies a desired target in t
148 a relative number. This can be expressed as pe
149 performance (infrastructure max). Below the no
150 level, desired performance expresses the avera
151 processor subject to hardware. Above the nomin
152 the processor must provide at least nominal pe
153 if current operating conditions allow.
154
155 Energy Performance Preference (EPP) (RW)
156 .........................................
157
158 This attribute provides a hint to the hardware
159 toward performance (0x0) or energy efficiency
160
161
162 Key Governors Support
163 =======================
164
165 ``amd-pstate`` can be used with all the (gener
166 by the ``scaling_available_governors`` policy
167 it is responsible for the configuration of pol
168 CPUs and provides the ``CPUFreq`` core (and th
169 to the policy objects) with accurate informati
170 operating frequencies supported by the hardwar
171 ``scaling_cur_freq`` information comes from th
172
173 ``amd-pstate`` mainly supports ``schedutil`` a
174 frequency control. It is to fine tune the proc
175 ``amd-pstate`` to the ``schedutil`` with CPU C
176 registers the adjust_perf callback to implemen
177 similar to CPPC. It is initialized by ``sugov_
178 CPU's update_util_data pointer to assign ``sug
179 utilization update callback function in the CP
180 will call ``cpufreq_update_util`` and assigns
181 to the ``struct sugov_cpu`` that the utilizati
182 Then, ``amd-pstate`` updates the desired perfo
183 scheduler assigned.
184
185 .. _processor_support:
186
187 Processor Support
188 =======================
189
190 The ``amd-pstate`` initialization will fail if
191 SBIOS does not exist in the detected processor
192 to check the existence of ``_CPC``. All Zen ba
193 ACPI hardware P-States function, so when ``amd
194 the kernel will fall back to initialize the ``
195
196 There are two types of hardware implementation
197 `Full MSR Support <perf_cap_>`_ and another is
198 <perf_cap_>`_. It can use the :c:macro:`X86_FE
199 indicate the different types. (For details, re
200 Reference (PPR) for AMD Family 19h Model 51h,
201 ``amd-pstate`` is to register different ``stat
202 hardware implementations.
203
204 Currently, some of the Zen2 and Zen3 processor
205 future, it will be supported on more and more
206
207 Full MSR Support
208 -----------------
209
210 Some new Zen3 processors such as Cezanne provi
211 while the :c:macro:`X86_FEATURE_CPPC` CPU feat
212 ``amd-pstate`` can handle the MSR register to
213 function in ``CPUFreq`` that can reduce the la
214 interrupt context. The functions with a ``psta
215 operations on MSR registers.
216
217 Shared Memory Support
218 ----------------------
219
220 If the :c:macro:`X86_FEATURE_CPPC` CPU feature
221 processor supports the shared memory solution.
222 uses the ``cppc_acpi`` helper methods to imple
223 that are defined on ``static_call``. The funct
224 represent the operations of ACPI CPPC helpers
225
226
227 AMD P-States and ACPI hardware P-States always
228 processor. But AMD P-States has the higher pri
229 with :c:macro:`MSR_AMD_CPPC_ENABLE` or ``cppc_
230 to the request from AMD P-States.
231
232
233 User Space Interface in ``sysfs`` - Per-policy
234 ==============================================
235
236 ``amd-pstate`` exposes several global attribut
237 control its functionality at the system level.
238 ``/sys/devices/system/cpu/cpufreq/policyX/`` d
239
240 root@hr-test1:/home/ray# ls /sys/devices/syst
241 /sys/devices/system/cpu/cpufreq/policy0/amd_p
242 /sys/devices/system/cpu/cpufreq/policy0/amd_p
243 /sys/devices/system/cpu/cpufreq/policy0/amd_p
244
245
246 ``amd_pstate_highest_perf / amd_pstate_max_fre
247
248 Maximum CPPC performance and CPU frequency tha
249 set, in percent of the maximum supported CPPC
250 performance supported in `AMD CPPC Performance
251 In some ASICs, the highest CPPC performance is
252 table, so we need to expose it to sysfs. If bo
253 still supported, this maximum frequency will b
254 ``cpuinfo``. On systems that support preferred
255 different values for some cores than others an
256 advertised by the platform at bootup.
257 This attribute is read-only.
258
259 ``amd_pstate_lowest_nonlinear_freq``
260
261 The lowest non-linear CPPC CPU frequency that
262 in percent of the maximum supported CPPC perfo
263 lowest non-linear performance in `AMD CPPC Per
264 <perf_cap_>`_.)
265 This attribute is read-only.
266
267 ``amd_pstate_hw_prefcore``
268
269 Whether the platform supports the preferred co
270 enabled. This attribute is read-only.
271
272 ``amd_pstate_prefcore_ranking``
273
274 The performance ranking of the core. This numb
275 larger numbers are preferred at the time of re
276 runtime based on platform conditions. This att
277
278 ``energy_performance_available_preferences``
279
280 A list of all the supported EPP preferences th
281 ``energy_performance_preference`` on this syst
282 These profiles represent different hints that
283 to the low-level firmware about the user's des
284 tradeoff. ``default`` represents the epp valu
285 firmware. This attribute is read-only.
286
287 ``energy_performance_preference``
288
289 The current energy performance preference can
290 and user can change current preference accordi
291 Please get all support profiles list from
292 ``energy_performance_available_preferences`` a
293 integer values defined between 0 to 255 when E
294 firmware, if EPP feature is disabled, driver w
295 This attribute is read-write.
296
297 ``boost``
298 The `boost` sysfs attribute provides control o
299 performance boost, allowing users to manage th
300 of the CPU. This attribute can be used to enab
301 on individual CPUs.
302
303 When the boost feature is enabled, the CPU can
304 beyond the base frequency, providing enhanced
305 On the other hand, disabling the boost feature
306 base frequency, which may be desirable in cert
307 efficiency or manage temperature.
308
309 To manipulate the `boost` attribute, users can
310 boost or `1` to enable it, for the respective
311 `/sys/devices/system/cpu/cpuX/cpufreq/boost`,
312
313 Other performance and frequency values can be
314 ``/sys/devices/system/cpu/cpuX/acpi_cppc/``, s
315
316
317 ``amd-pstate`` vs ``acpi-cpufreq``
318 ======================================
319
320 On the majority of AMD platforms supported by
321 provided by the platform firmware are used for
322 only provide 3 P-states on AMD processors.
323 However, on modern AMD APU and CPU series, har
324 Processor Performance Control according to the
325 for AMD platforms. That is, fine-grained and c
326 instead of the legacy hardware P-states. ``amd
327 module which supports the new AMD P-States mec
328 platforms. The AMD P-States mechanism is the m
329 efficiency frequency management method on AMD
330
331
332 ``amd-pstate`` Driver Operation Modes
333 ======================================
334
335 ``amd_pstate`` CPPC has 3 operation modes: aut
336 non-autonomous (passive) mode and guided auton
337 Active/passive/guided mode can be chosen by di
338
339 - In autonomous mode, platform ignores the des
340 and takes into account only the values set t
341 performance preference registers.
342 - In non-autonomous mode, platform gets desire
343 from OS directly through Desired Performance
344 - In guided-autonomous mode, platform sets ope
345 autonomously according to the current worklo
346 OS through min and max performance registers
347
348 Active Mode
349 ------------
350
351 ``amd_pstate=active``
352
353 This is the low-level firmware control mode wh
354 driver with ``amd_pstate=active`` passed to th
355 In this mode, ``amd_pstate_epp`` driver provid
356 wants to bias toward performance (0x0) or ener
357 then CPPC power algorithm will calculate the r
358 cores frequency according to the power supply
359 hardware conditions.
360
361 Passive Mode
362 ------------
363
364 ``amd_pstate=passive``
365
366 It will be enabled if the ``amd_pstate=passive
367 In this mode, ``amd_pstate`` driver software s
368 performance scale as a relative number. This c
369 performance (infrastructure max). Below the no
370 desired performance expresses the average perf
371 to the Performance Reduction Tolerance registe
372 processor must provide at least nominal perfor
373 operating conditions allow.
374
375 Guided Mode
376 -----------
377
378 ``amd_pstate=guided``
379
380 If ``amd_pstate=guided`` is passed to kernel c
381 is activated. In this mode, driver requests m
382 level and the platform autonomously selects a
383 and appropriate to the current workload.
384
385 ``amd-pstate`` Preferred Core
386 =================================
387
388 The core frequency is subjected to the process
389 Not all cores are able to reach the maximum fr
390 infrastructure limits. Consequently, AMD has r
391 maximum frequency of a part. This means that a
392 maximum frequency. To find the best process sc
393 scenario, OS needs to know the core ordering i
394 highest performance capability register of the
395
396 ``amd-pstate`` preferred core enables the sche
397 cores that can achieve a higher frequency with
398 core rankings can dynamically change based on
399 thermals and ageing.
400
401 The priority metric will be initialized by the
402 driver will also determine whether or not ``am
403 supported by the platform.
404
405 ``amd-pstate`` driver will provide an initial
406 The platform uses the CPPC interfaces to commu
407 operating system and scheduler to make sure th
408 with highest performance firstly for schedulin
409 driver receives a message with the highest per
410 update the core ranking and set the cpu's prio
411
412 ``amd-pstate`` Preferred Core Switch
413 =====================================
414 Kernel Parameters
415 -----------------
416
417 ``amd-pstate`` peferred core`` has two states:
418 Enable/disable states can be chosen by differe
419 Default enable ``amd-pstate`` preferred core.
420
421 ``amd_prefcore=disable``
422
423 For systems that support ``amd-pstate`` prefer
424 always be advertised by the platform. But OS c
425 kernel parameter ``amd_prefcore=disable``.
426
427 User Space Interface in ``sysfs`` - General
428 ===========================================
429
430 Global Attributes
431 -----------------
432
433 ``amd-pstate`` exposes several global attribut
434 control its functionality at the system level.
435 ``/sys/devices/system/cpu/amd_pstate/`` direct
436
437 ``status``
438 Operation mode of the driver: "active"
439
440 "active"
441 The driver is functional and i
442
443 "passive"
444 The driver is functional and i
445
446 "guided"
447 The driver is functional and i
448
449 "disable"
450 The driver is unregistered and
451
452 This attribute can be written to in or
453 operation mode or to unregister it. T
454 one of the possible values of it and,
455 these values to the sysfs file will ca
456 to the operation mode represented by t
457 unregistered in the "disable" case.
458
459 ``prefcore``
460 Preferred core state of the driver: "e
461
462 "enabled"
463 Enable the ``amd-pstate`` pref
464
465 "disabled"
466 Disable the ``amd-pstate`` pre
467
468
469 This attribute is read-only to check t
470 by the kernel parameter.
471
472 ``cpupower`` tool support for ``amd-pstate``
473 ==============================================
474
475 ``amd-pstate`` is supported by the ``cpupower`
476 frequency information. Development is in progr
477 operations for the new ``amd-pstate`` module w
478
479 root@hr-test1:/home/ray# cpupower frequency-i
480 analyzing CPU 0:
481 driver: amd-pstate
482 CPUs which run at the same hardware frequen
483 CPUs which need to have their frequency coo
484 maximum transition latency: 131 us
485 hardware limits: 400 MHz - 4.68 GHz
486 available cpufreq governors: ondemand conse
487 current policy: frequency should be within
488 The governor "schedutil" ma
489 within this range.
490 current CPU frequency: Unable to call hardw
491 current CPU frequency: 4.02 GHz (asserted b
492 boost state support:
493 Supported: yes
494 Active: yes
495 AMD PSTATE Highest Performance: 166. Maxi
496 AMD PSTATE Nominal Performance: 117. Nomi
497 AMD PSTATE Lowest Non-linear Performance:
498 AMD PSTATE Lowest Performance: 15. Lowest
499
500
501 Diagnostics and Tuning
502 =======================
503
504 Trace Events
505 --------------
506
507 There are two static trace events that can be
508 diagnostics. One of them is the ``cpu_frequenc
509 by ``CPUFreq``, and the other one is the ``amd
510 specific to ``amd-pstate``. The following seq
511 be used to enable them and see their output (i
512 configured to support event tracing). ::
513
514 root@hr-test1:/home/ray# cd /sys/kernel/traci
515 root@hr-test1:/sys/kernel/tracing# echo 1 > e
516 root@hr-test1:/sys/kernel/tracing# cat trace
517 # tracer: nop
518 #
519 # entries-in-buffer/entries-written: 47827/42
520 #
521 # _-----=> irq
522 # / _----=> nee
523 # | / _---=> har
524 # || / _--=> pre
525 # ||| / dela
526 # TASK-PID CPU# |||| TIMESTA
527 # | | | |||| |
528 <idle>-0 [015] dN... 4995.979
529 <idle>-0 [007] d.h.. 4995.979
530 cat-2161 [000] d.... 4995.980
531 sshd-2125 [004] d.s.. 4995.980
532 <idle>-0 [007] d.s.. 4995.980
533 <idle>-0 [003] d.s.. 4995.980
534 <idle>-0 [011] d.s.. 4995.980
535
536 The ``cpu_frequency`` trace event will be trig
537 governor (for the policies it is attached to),
538 policies with other scaling governors).
539
540
541 Tracer Tool
542 -------------
543
544 ``amd_pstate_tracer.py`` can record and parse
545 generate performance plots. This utility can b
546 performance of ``amd-pstate`` driver. The trac
547 pstate tracer.
548
549 Tracer tool located in ``linux/tools/power/x86
550 used in two ways. If trace file is available,
551 with command ::
552
553 ./amd_pstate_trace.py [-c cpus] -t <trace_fil
554
555 Or generate trace file with root privilege, th
556
557 sudo ./amd_pstate_trace.py [-c cpus] -n <test
558
559 The test result can be found in ``results/test
560 about part of the output. ::
561
562 common_cpu common_secs common_usecs min_pe
563 CPU_005 712 116384 39
564 CPU_006 712 116408 39
565
566 Unit Tests for amd-pstate
567 -------------------------
568
569 ``amd-pstate-ut`` is a test module for testing
570
571 * It can help all users to verify their proce
572
573 * Kernel can have a basic function test to av
574
575 * We can introduce more functional or perform
576
577 1. Test case descriptions
578
579 1). Basic tests
580
581 Test prerequisite and basic functions
582
583 +---------+---------------------------
584 | Index | Functions
585 +=========+===========================
586 | 1 | amd_pstate_ut_acpi_cpc_val
587 | |
588 | |
589 +---------+---------------------------
590 | 2 | amd_pstate_ut_check_enable
591 | |
592 | |
593 | |
594 | |
595 | |
596 +---------+---------------------------
597 | 3 | amd_pstate_ut_check_perf
598 | |
599 +---------+---------------------------
600 | 4 | amd_pstate_ut_check_freq
601 | |
602 | |
603 | |
604 | |
605 +---------+---------------------------
606
607 2). Tbench test
608
609 Test and monitor the cpu changes when
610 These changes include desire performan
611 The specified governor is ondemand or
612 Tbench can also be tested on the ``acp
613
614 3). Gitsource test
615
616 Test and monitor the cpu changes when
617 These changes include desire performan
618 The specified governor is ondemand or
619 Gitsource can also be tested on the ``
620
621 #. How to execute the tests
622
623 We use test module in the kselftest framewo
624 We create ``amd-pstate-ut`` module and tie
625 details refer to Linux Kernel Selftests [4]
626
627 1). Build
628
629 + open the :c:macro:`CONFIG_X86_AMD_PS
630 + set the :c:macro:`CONFIG_X86_AMD_PST
631 + make project
632 + make selftest ::
633
634 $ cd linux
635 $ make -C tools/testing/selftests
636
637 + make perf ::
638
639 $ cd tools/perf/
640 $ make
641
642
643 2). Installation & Steps ::
644
645 $ make -C tools/testing/selftests inst
646 $ cp tools/perf/perf /usr/bin/perf
647 $ sudo ./kselftest/run_kselftest.sh -c
648
649 3). Specified test case ::
650
651 $ cd ~/kselftest/amd-pstate
652 $ sudo ./run.sh -t basic
653 $ sudo ./run.sh -t tbench
654 $ sudo ./run.sh -t tbench -m acpi-cpuf
655 $ sudo ./run.sh -t gitsource
656 $ sudo ./run.sh -t gitsource -m acpi-c
657 $ ./run.sh --help
658 ./run.sh: illegal option -- -
659 Usage: ./run.sh [OPTION...]
660 [-h <help>]
661 [-o <output-file-for-dump>]
662 [-c <all: All testing,
663 basic: Basic testing,
664 tbench: Tbench testing,
665 gitsource: Gitsource test
666 [-t <tbench time limit>]
667 [-p <tbench process number>]
668 [-l <loop times for tbench>]
669 [-i <amd tracer interval>]
670 [-m <comparative test: acpi-cp
671
672
673 4). Results
674
675 + basic
676
677 When you finish test, you will get th
678
679 $ dmesg | grep "amd_pstate_ut" | tee
680 [12977.570663] amd_pstate_ut: 1 a
681 [12977.570673] amd_pstate_ut: 2 a
682 [12977.571207] amd_pstate_ut: 3 a
683 [12977.571212] amd_pstate_ut: 4 a
684
685 + tbench
686
687 When you finish test, you will get se
688 The selftest.tbench.csv file contains
689 The png images shows the performance,
690 Open selftest.tbench.csv :
691
692 +------------------------------------
693 + Governor
694 +------------------------------------
695 + Unit
696 +====================================
697 + amd-pstate-ondemand
698 +------------------------------------
699 + amd-pstate-ondemand
700 +------------------------------------
701 + amd-pstate-ondemand
702 +------------------------------------
703 + amd-pstate-ondemand
704 +------------------------------------
705 + amd-pstate-schedutil
706 +------------------------------------
707 + amd-pstate-schedutil
708 +------------------------------------
709 + amd-pstate-schedutil
710 +------------------------------------
711 + amd-pstate-schedutil
712 +------------------------------------
713 + acpi-cpufreq-ondemand
714 +------------------------------------
715 + acpi-cpufreq-ondemand
716 +------------------------------------
717 + acpi-cpufreq-ondemand
718 +------------------------------------
719 + acpi-cpufreq-ondemand
720 +------------------------------------
721 + acpi-cpufreq-schedutil
722 +------------------------------------
723 + acpi-cpufreq-schedutil
724 +------------------------------------
725 + acpi-cpufreq-schedutil
726 +------------------------------------
727 + acpi-cpufreq-schedutil
728 +------------------------------------
729 + acpi-cpufreq-ondemand VS acpi-cpufr
730 +------------------------------------
731 + amd-pstate-ondemand VS amd-pstate-s
732 +------------------------------------
733 + acpi-cpufreq-ondemand VS amd-pstate
734 +------------------------------------
735 + acpi-cpufreq-schedutil VS amd-pstat
736 +------------------------------------
737
738 + gitsource
739
740 When you finish test, you will get se
741 The selftest.gitsource.csv file conta
742 The png images shows the performance,
743 Open selftest.gitsource.csv :
744
745 +------------------------------------
746 + Governor
747 +------------------------------------
748 + Unit
749 +====================================
750 + amd-pstate-ondemand
751 +------------------------------------
752 + amd-pstate-ondemand
753 +------------------------------------
754 + amd-pstate-ondemand
755 +------------------------------------
756 + amd-pstate-ondemand
757 +------------------------------------
758 + amd-pstate-schedutil
759 +------------------------------------
760 + amd-pstate-schedutil
761 +------------------------------------
762 + amd-pstate-schedutil
763 +------------------------------------
764 + amd-pstate-schedutil
765 +------------------------------------
766 + acpi-cpufreq-ondemand
767 +------------------------------------
768 + acpi-cpufreq-ondemand
769 +------------------------------------
770 + acpi-cpufreq-ondemand
771 +------------------------------------
772 + acpi-cpufreq-ondemand
773 +------------------------------------
774 + acpi-cpufreq-schedutil
775 +------------------------------------
776 + acpi-cpufreq-schedutil
777 +------------------------------------
778 + acpi-cpufreq-schedutil
779 +------------------------------------
780 + acpi-cpufreq-schedutil
781 +------------------------------------
782 + acpi-cpufreq-ondemand VS acpi-cpufr
783 +------------------------------------
784 + amd-pstate-ondemand VS amd-pstate-s
785 +------------------------------------
786 + acpi-cpufreq-ondemand VS amd-pstate
787 +------------------------------------
788 + acpi-cpufreq-schedutil VS amd-pstat
789 +------------------------------------
790
791 Reference
792 ===========
793
794 .. [1] AMD64 Architecture Programmer's Manual
795 https://www.amd.com/system/files/TechDo
796
797 .. [2] Advanced Configuration and Power Interf
798 https://uefi.org/sites/default/files/re
799
800 .. [3] Processor Programming Reference (PPR) f
801 https://www.amd.com/system/files/TechDo
802
803 .. [4] Linux Kernel Selftests,
804 https://www.kernel.org/doc/html/latest/
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