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Message-ID: <1d713fe5-485b-4aeb-a279-13fce93692fc@arm.com>
Date: Tue, 18 Feb 2025 21:17:27 +0000
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
Linux PM <linux-pm@...r.kernel.org>, dsmythies@...us.net
Cc: LKML <linux-kernel@...r.kernel.org>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
Aboorva Devarajan <aboorvad@...ux.ibm.com>
Subject: Re: [RFT][PATCH v1 0/5] cpuidle: menu: Avoid discarding useful
information when processing recent idle intervals
On 2/10/25 14:15, Christian Loehle wrote:
> On 2/6/25 14:21, Rafael J. Wysocki wrote:
>> Hi Everyone,
>>
>> This work had been triggered by a report that commit 0611a640e60a ("eventpoll:
>> prefer kfree_rcu() in __ep_remove()") had caused the critical-jOPS metric of
>> the SPECjbb 2015 benchmark [1] to drop by around 50% even though it generally
>> reduced kernel overhead. Indeed, it was found during further investigation
>> that the total interrupt rate while running the SPECjbb workload had fallen as
>> a result of that commit by 55% and the local timer interrupt rate had fallen by
>> almost 80%.
>>
>> That turned out to cause the menu cpuidle governor to select the deepest idle
>> state supplied by the cpuidle driver (intel_idle) much more often which added
>> significantly more idle state latency to the workload and that led to the
>> decrease of the critical-jOPS score.
>>
>> Interestingly enough, this problem was not visible when the teo cpuidle
>> governor was used instead of menu, so it appeared to be specific to the
>> latter. CPU wakeup event statistics collected while running the workload
>> indicated that the menu governor was effectively ignoring non-timer wakeup
>> information and all of its idle state selection decisions appeared to be
>> based on timer wakeups only. Thus, it appeared that the reduction of the
>> local timer interrupt rate caused the governor to predict a idle duration
>> much more often while running the workload and the deepest idle state was
>> selected significantly more often as a result of that.
>>
>> A subsequent inspection of the get_typical_interval() function in the menu
>> governor indicated that it might return UINT_MAX too often which then caused
>> the governor's decisions to be based entirely on information related to timers.
>>
>> Generally speaking, UINT_MAX is returned by get_typical_interval() if it
>> cannot make a prediction based on the most recent idle intervals data with
>> sufficiently high confidence, but at least in some cases this means that
>> useful information is not taken into account at all which may lead to
>> significant idle state selection mistakes. Moreover, this is not really
>> unlikely to happen.
>>
>> One issue with get_typical_interval() is that, when it eliminates outliers from
>> the sample set in an attempt to reduce the standard deviation (and so improve
>> the prediction confidence), it does that by dropping high-end samples only,
>> while samples at the low end of the set are retained. However, the samples
>> at the low end very well may be the outliers and they should be eliminated
>> from the sample set instead of the high-end samples. Accordingly, the
>> likelihood of making a meaningful idle duration prediction can be improved
>> by making it also eliminate low-end samples if they are farther from the
>> average than high-end samples. This is done in patch [4/5].
>>
>> Another issue is that get_typical_interval() gives up after eliminating 1/4
>> of the samples if the standard deviation is still not as low as desired (within
>> 1/6 of the average or within 20 us if the average is close to 0), but the
>> remaining samples in the set still represent useful information at that point
>> and discarding them altogether may lead to suboptimal idle state selection.
>>
>> For instance, the largest idle duration value in the get_typical_interval()
>> data set is the maximum idle duration observed recently and it is likely that
>> the upcoming idle duration will not exceed it. Therefore, in the absence of
>> a better choice, this value can be used as an upper bound on the target
>> residency of the idle state to select. Patch [5/5] works along these lines,
>> but it takes the maximum data point remaining after the elimination of
>> outliers.
>>
>> The first two patches in the series are straightforward cleanups (in fact,
>> the first patch is kind of reversed by patch [4/5], but it is there because
>> it can be applied without the latter) and patch [3/5] is a cosmetic change
>> made in preparation for the subsequent ones.
>>
>> This series turns out to restore the SPECjbb critical-jOPS metric on affected
>> systems to the level from before commit 0611a640e60a and it also happens to
>> increase its max-jOPS metric by around 3%.
>>
>> For easier reference/testing it is present in the git branch at
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/log/?h=experimental/menu
>>
>> based on the cpuidle material that went into 6.14-rc1.
>>
>> If possible, please let me know if it works for you.
>>
>> Thanks!
>>
>>
>> [1] Link: https://www.spec.org/jbb2015/
Another dump for x86 idle this time, tldr: no worrying idle/power numbers
teo 0 121.76 12202 813 0.067 390 423
teo 1 158.53 8223 536 0.065 328 208
teo 2 219.37 8373 527 0.063 294 233
teo 3 220.7 8241 538 0.065 340 198
teo 4 211.8 7923 442 0.056 268 174
menu 0 151.63 8185 326 0.040 308 18
menu 1 183.45 8873 364 0.041 334 30
menu 2 171.96 8633 380 0.044 369 11
menu 3 164.95 8451 358 0.042 330 28
menu 4 175.87 8273 340 0.041 317 23
menu-1 0 119.77 9041 394 0.044 356 38
menu-1 1 145.73 8603 335 0.039 293 42
menu-1 2 157.89 8345 321 0.038 276 45
menu-1 3 119.13 8447 346 0.041 290 56
menu-1 4 142.77 8331 331 0.040 312 19
menu-2 0 159.81 8653 342 0.040 296 46
menu-2 1 165.01 8421 307 0.036 282 25
menu-2 2 225.06 8647 376 0.043 317 59
menu-2 3 232.13 8095 358 0.044 325 33
menu-2 4 150.79 8231 323 0.039 299 24
menu-3 0 168.87 8153 355 0.044 330 25
menu-3 1 187.68 9143 405 0.044 338 67
menu-3 2 129.77 9705 384 0.040 301 83
menu-3 3 152.49 9679 469 0.048 374 95
menu-3 4 131.0 9077 321 0.035 283 38
menu-4 0 116.68 9107 373 0.041 333 40
menu-4 1 164.1 8655 297 0.034 287 10
menu-4 2 157.52 8009 300 0.037 297 3
menu-4 3 138.47 8567 345 0.040 341 4
menu-4 4 130.84 8027 324 0.040 316 8
menu-5 0 139.77 8533 327 0.038 317 10
menu-5 1 157.22 9127 433 0.047 373 60
menu-5 2 144.54 8313 329 0.040 311 18
menu-5 3 151.55 8675 316 0.036 301 15
menu-5 4 137.49 8823 354 0.040 336 18
menu 0 128.97 8383 329 0.039 284 45
menu 1 141.97 8945 402 0.045 344 58
menu 2 88.16 8829 368 0.042 307 61
menu 3 81.49 9165 430 0.047 371 59
menu 4 107.58 9193 401 0.044 335 66
teo 0 149.28 8399 521 0.062 287 234
teo 1 105.61 8717 563 0.065 306 257
teo 2 116.65 7893 550 0.070 284 266
teo 3 119.57 8259 489 0.059 282 207
teo 4 187.64 7897 471 0.060 303 168
And the rk3399 numbers as promised, just like rk3588 we see much better
IO performance (menu-5) without significant worse idle decisions:
device gov iter iops idles idle_misses idle_miss_ratio belows aboves
mapper/dm-slow teo 0 461 102980 32260 0.313 6036 26224
mapper/dm-slow teo 1 461 100698 31149 0.309 5796 25353
mapper/dm-slow teo 2 461 100346 32840 0.327 6022 26818
mapper/dm-slow teo 3 461 98450 31513 0.320 5129 26384
mapper/dm-slow teo 4 461 98689 29982 0.304 3937 26045
mapper/dm-slow menu 0 461 97860 22520 0.230 5505 17015
mapper/dm-slow menu 1 461 98002 20858 0.213 3596 17262
mapper/dm-slow menu 2 461 100046 22523 0.225 5333 17190
mapper/dm-slow menu 3 461 95020 20827 0.219 4069 16758
mapper/dm-slow menu 4 461 98040 22302 0.227 5498 16804
mapper/dm-slow menu-1 0 461 98186 20648 0.210 3210 17438
mapper/dm-slow menu-1 1 461 94360 20297 0.215 4184 16113
mapper/dm-slow menu-1 2 461 98818 21680 0.219 4750 16930
mapper/dm-slow menu-1 3 461 97822 20605 0.211 3469 17136
mapper/dm-slow menu-1 4 461 100748 21740 0.216 4403 17337
mapper/dm-slow menu-2 0 461 94388 20289 0.215 3449 16840
mapper/dm-slow menu-2 1 460 89124 18897 0.212 2401 16496
mapper/dm-slow menu-2 2 461 94932 20692 0.218 2949 17743
mapper/dm-slow menu-2 3 461 95270 20612 0.216 3048 17564
mapper/dm-slow menu-2 4 461 101954 23493 0.230 5978 17515
mapper/dm-slow menu-3 0 461 98452 21161 0.215 4247 16914
mapper/dm-slow menu-3 1 461 100342 21035 0.210 3891 17144
mapper/dm-slow menu-3 2 461 101156 23322 0.231 5924 17398
mapper/dm-slow menu-3 3 461 98052 20862 0.213 3927 16935
mapper/dm-slow menu-3 4 461 97746 20977 0.215 3706 17271
mapper/dm-slow menu-4 0 461 99826 23727 0.238 5055 18672
mapper/dm-slow menu-4 1 461 101686 24859 0.244 5175 19684
mapper/dm-slow menu-4 2 461 99934 23568 0.236 4477 19091
mapper/dm-slow menu-4 3 461 97298 22142 0.228 3644 18498
mapper/dm-slow menu-4 4 461 98546 24023 0.244 5086 18937
mapper/dm-slow menu-5 0 461 100545 22833 0.227 3830 19003
mapper/dm-slow menu-5 1 461 100827 23999 0.238 5217 18782
mapper/dm-slow menu-5 2 461 97044 22628 0.233 2910 19718
mapper/dm-slow menu-5 3 461 100234 23303 0.232 4819 18484
mapper/dm-slow menu-5 4 461 102358 24488 0.239 4770 19718
mapper/dm-slow menu 0 461 97008 21114 0.218 4540 16574
mapper/dm-slow menu 1 461 96088 21470 0.223 3650 17820
mapper/dm-slow menu 2 461 99008 21019 0.212 3405 17614
mapper/dm-slow menu 3 461 96608 20145 0.209 3729 16416
mapper/dm-slow menu 4 461 83152 17469 0.210 2426 15043
mapper/dm-slow teo 0 461 99340 32077 0.323 5772 26305
mapper/dm-slow teo 1 461 98694 29426 0.298 3585 25841
mapper/dm-slow teo 2 461 100294 29810 0.297 3561 26249
mapper/dm-slow teo 3 461 98726 29496 0.299 3644 25852
mapper/dm-slow teo 4 461 101424 32654 0.322 6029 26625
mmcblk1 teo 0 2016 559362 29994 0.054 2896 27098
mmcblk1 teo 1 2037 562153 30001 0.053 3171 26830
mmcblk1 teo 2 2016 557360 30185 0.054 2986 27199
mmcblk1 menu 0 1279 335364 103600 0.309 87662 15938
mmcblk1 menu 1 1292 342036 105446 0.308 89031 16415
mmcblk1 menu 2 1294 352954 108588 0.308 90420 18168
mmcblk1 menu-1 0 1271 331220 103163 0.311 87602 15561
mmcblk1 menu-1 1 1291 350084 108982 0.311 90670 18312
mmcblk1 menu-1 2 1284 346412 107494 0.310 89899 17595
mmcblk1 menu-2 0 1306 344316 106253 0.309 89650 16603
mmcblk1 menu-2 1 1278 345684 107893 0.312 90292 17601
mmcblk1 menu-2 2 1268 334528 104494 0.312 88457 16037
mmcblk1 menu-3 0 1270 333456 104160 0.312 88392 15768
mmcblk1 menu-3 1 1273 338328 105477 0.312 88798 16679
mmcblk1 menu-3 2 1280 337002 104623 0.310 88516 16107
mmcblk1 menu-4 0 1311 344896 104192 0.302 87051 17141
mmcblk1 menu-4 1 1292 343878 106459 0.310 88297 18162
mmcblk1 menu-4 2 1286 340172 105502 0.310 87753 17749
mmcblk1 menu-5 0 2006 550266 24981 0.045 6762 18219
mmcblk1 menu-5 1 1997 553590 26974 0.049 6955 20019
mmcblk1 menu-5 2 1994 539494 17652 0.033 3903 13749
mmcblk2 teo 0 5691 820134 29346 0.036 3078 26268
mmcblk2 teo 1 5684 856976 23202 0.027 1908 21294
mmcblk2 teo 2 5783 824666 13984 0.017 3938 10046
mmcblk2 menu 0 2770 433474 144860 0.334 127466 17394
mmcblk2 menu 1 3308 367848 89597 0.244 72668 16929
mmcblk2 menu 2 2882 422844 133523 0.316 117170 16353
mmcblk2 menu-1 0 3323 394674 115764 0.293 99328 16436
mmcblk2 menu-1 1 2778 420262 139538 0.332 122356 17182
mmcblk2 menu-1 2 2895 400774 124841 0.311 109572 15269
mmcblk2 menu-2 0 2679 429818 148494 0.345 131513 16981
mmcblk2 menu-2 1 3162 363888 96102 0.264 79200 16902
mmcblk2 menu-2 2 2684 422324 144606 0.342 128528 16078
mmcblk2 menu-3 0 2953 392124 118629 0.303 101068 17561
mmcblk2 menu-3 1 3003 402614 120567 0.299 103321 17246
mmcblk2 menu-3 2 2858 422576 136118 0.322 119485 16633
mmcblk2 menu-4 0 3288 436860 118566 0.271 100329 18237
mmcblk2 menu-4 1 3062 462484 139897 0.302 121424 18473
mmcblk2 menu-4 2 3257 424458 115493 0.272 97739 17754
mmcblk2 menu-5 0 5316 573050 52502 0.092 33285 19217
mmcblk2 menu-5 1 5446 825538 44073 0.053 24355 19718
mmcblk2 menu-5 2 5292 796000 52828 0.066 38640 14188
nvme0n1 teo 0 11371 807338 29879 0.037 2961 26918
nvme0n1 teo 1 11557 815682 29116 0.036 2947 26169
nvme0n1 teo 2 11424 810108 29800 0.037 2953 26847
nvme0n1 menu 0 7754 574116 93148 0.162 76482 16666
nvme0n1 menu 1 8371 618954 95502 0.154 77657 17845
nvme0n1 menu 2 5111 412030 73440 0.178 55997 17443
nvme0n1 menu-1 0 6628 506618 91832 0.181 71427 20405
nvme0n1 menu-1 1 4923 390294 68772 0.176 52880 15892
nvme0n1 menu-1 2 5015 396160 68840 0.174 52867 15973
nvme0n1 menu-2 0 7883 589296 97497 0.165 79635 17862
nvme0n1 menu-2 1 6465 493796 81561 0.165 64629 16932
nvme0n1 menu-2 2 5363 430614 75499 0.175 57528 17971
nvme0n1 menu-3 0 5090 415018 74191 0.179 56015 18176
nvme0n1 menu-3 1 4919 401452 71994 0.179 54457 17537
nvme0n1 menu-3 2 5183 413186 74199 0.180 57542 16657
nvme0n1 menu-4 0 5402 424860 67413 0.159 49399 18014
nvme0n1 menu-4 1 5343 420538 67713 0.161 49826 17887
nvme0n1 menu-4 2 9151 669840 107892 0.161 87774 20118
nvme0n1 menu-5 0 10475 741376 20204 0.027 1827 18377
nvme0n1 menu-5 1 10603 747262 19228 0.026 1489 17739
nvme0n1 menu-5 2 11658 824996 22954 0.028 2631 20323
sda teo 0 2328 1334552 48960 0.037 20922 28038
sda teo 1 2328 1267840 37740 0.030 11934 25806
sda teo 2 2394 1360679 21853 0.016 3394 18459
sda menu 0 1004 587054 198775 0.339 184002 14773
sda menu 1 1205 663838 209623 0.316 193325 16298
sda menu 2 1117 615382 208813 0.339 191893 16920
sda menu-1 0 1103 627838 212955 0.339 195703 17252
sda menu-1 1 1024 611658 221754 0.363 203710 18044
sda menu-1 2 1209 639008 180597 0.283 163837 16760
sda menu-2 0 1200 655398 205664 0.314 190750 14914
sda menu-2 1 1100 582222 201983 0.347 185874 16109
sda menu-2 2 1124 602988 199623 0.331 183798 15825
sda menu-3 0 1089 612112 211470 0.345 195156 16314
sda menu-3 1 1077 613556 213484 0.348 196839 16645
sda menu-3 2 1157 636904 195439 0.307 179535 15904
sda menu-4 0 1126 643468 208132 0.323 189334 18798
sda menu-4 1 1112 634480 216012 0.340 196841 19171
sda menu-4 2 1190 594398 196059 0.330 176190 19869
sda menu-5 0 2074 1134718 81294 0.072 61820 19474
sda menu-5 1 2179 1249056 76679 0.061 55461 21218
sda menu-5 2 2075 1183214 124075 0.105 101650 22425
nullb0 teo 0 104833 85906 29085 0.339 3409 25676
nullb0 teo 1 103787 88419 29833 0.337 2980 26853
nullb0 teo 2 104611 86284 29390 0.341 3315 26075
nullb0 menu 0 103671 87146 20514 0.235 2643 17871
nullb0 menu 1 104380 70086 16855 0.240 1642 15213
nullb0 menu 2 103249 81414 19403 0.238 2274 17129
nullb0 menu-1 0 103424 86984 20448 0.235 2617 17831
nullb0 menu-1 1 103857 85658 20840 0.243 2544 18296
nullb0 menu-1 2 103907 86644 20639 0.238 2586 18053
nullb0 menu-2 0 103668 82558 20053 0.243 2655 17398
nullb0 menu-2 1 104277 86914 20472 0.236 2593 17879
nullb0 menu-2 2 103697 82952 20221 0.244 2410 17811
nullb0 menu-3 0 103696 86534 20782 0.240 2968 17814
nullb0 menu-3 1 103996 81902 19795 0.242 2773 17022
nullb0 menu-3 2 103790 82474 20058 0.243 2344 17714
nullb0 menu-4 0 103288 87475 22688 0.259 2596 20092
nullb0 menu-4 1 103848 70906 18106 0.255 1557 16549
nullb0 menu-4 2 104141 84528 22147 0.262 2969 19178
nullb0 menu-5 0 103812 79234 17989 0.227 1302 16687
nullb0 menu-5 1 104334 87752 22878 0.261 2511 20367
nullb0 menu-5 2 104059 88681 22765 0.257 3030 19735
mtdblock3 teo 0 257 604294 17359 0.029 3241 14118
mtdblock3 teo 1 256 332344 31631 0.095 4644 26987
mtdblock3 teo 2 257 549736 29559 0.054 2841 26718
mtdblock3 menu 0 148 417388 134505 0.322 118487 16018
mtdblock3 menu 1 137 422132 149336 0.354 132655 16681
mtdblock3 menu 2 194 223808 59631 0.266 43076 16555
mtdblock3 menu-1 0 145 529186 143789 0.272 129433 14356
mtdblock3 menu-1 1 147 452302 140418 0.310 125009 15409
mtdblock3 menu-1 2 138 415152 146470 0.353 130607 15863
mtdblock3 menu-2 0 155 365750 118483 0.324 102676 15807
mtdblock3 menu-2 1 165 316818 101968 0.322 85597 16371
mtdblock3 menu-2 2 143 515664 126014 0.244 115854 10160
mtdblock3 menu-3 0 135 488188 150917 0.309 136442 14475
mtdblock3 menu-3 1 125 437774 158893 0.363 143319 15574
mtdblock3 menu-3 2 138 433332 152457 0.352 135017 17440
mtdblock3 menu-4 0 173 314250 101648 0.323 81511 20137
mtdblock3 menu-4 1 149 489030 139551 0.285 124126 15425
mtdblock3 menu-4 2 148 381488 133543 0.350 115885 17658
mtdblock3 menu-5 0 222 430158 63885 0.149 45240 18645
mtdblock3 menu-5 1 218 752248 80500 0.107 66453 14047
mtdblock3 menu-5 2 203 528828 105885 0.200 89573 1631
And finally a longer firefox youtube 4k playback (10mins) on x86:
device gov iter Joules idles idle_misses idle_miss_ratio belows aboves
menu 0 1064.48 357559 106048 0.297 105920 128
menu 1 1029.85 345569 104050 0.301 103938 112
menu 2 1105.93 347105 104958 0.302 104885 73
menu 3 1085.86 347365 106061 0.305 106001 60
menu 4 1115.24 352609 107913 0.306 107812 101
menu-5 0 1139.09 345827 90172 0.261 89609 563
menu-5 1 1111.58 335521 88953 0.265 88904 49
menu-5 2 1093.73 328645 85949 0.262 85839 110
menu-5 3 1036.69 330547 86163 0.261 86077 86
menu-5 4 1117.31 316143 81707 0.258 81580 127
menu 0 1099.72 353895 106574 0.301 106523 51
menu 1 1148.44 357867 107578 0.301 107369 209
menu 2 1098.15 341957 101995 0.298 101870 125
menu 3 1124.41 350423 105592 0.301 105481 111
menu 4 1185.94 366799 111132 0.303 111029 103
menu-5 0 1129.85 332413 86991 0.262 86885 106
menu-5 1 1086.59 318221 82020 0.258 81924 96
menu-5 2 1063.5 320273 83099 0.259 83048 51
menu-5 3 1070.7 331179 85998 0.260 85839 159
menu-5 4 1067.82 322689 83634 0.259 83548 86
Significantly improving idle miss belows.
I'll do the Android tests, but that is very unlikely to show something this
doesn't (there's only one non-WFI idle state and most workloads are intercept
heavy, so if anything menu-5 should improve the overall situation.)
Feel free to already add:
Tested-by: Christian Loehle <christian.loehle@....com>
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