Re: [PATCH 2/2] sched/eevdf: Use sched_attr::sched_runtime to set request/slice suggestion

[Mike Galbraith]

On Fri, 2023-09-15 at 14:43 +0200, peterz@xxxxxxxxxxxxx wrote:
> Allow applications to directly set a suggested request/slice length using
> sched_attr::sched_runtime.

I met an oddity while fiddling to see what a custom slice would do for
cyclictest, it seeming to be reasonable target.  $subject seems to be
working fine per live peek with crash, caveat being it's not alone in
otherwise virgin source...

homer:..kernel/linux-tip # make -j8 vmlinux && killall cyclictest

Elsewhere, post build/kill...

instance-a, stock
homer:/root # cyclictest -Smq
# /dev/cpu_dma_latency set to 0us
T: 0 (17763) P: 0 I:1000 C: 297681 Min:      2 Act:   51 Avg:   66 Max:   10482
T: 1 (17764) P: 0 I:1500 C: 198639 Min:      2 Act: 3159 Avg:   70 Max:    9054
T: 2 (17765) P: 0 I:2000 C: 149075 Min:      2 Act:   52 Avg:   78 Max:    8190
T: 3 (17766) P: 0 I:2500 C: 119867 Min:      2 Act:   55 Avg:   77 Max:    8328
T: 4 (17767) P: 0 I:3000 C:  99888 Min:      2 Act:   51 Avg:   90 Max:    8483
T: 5 (17768) P: 0 I:3500 C:  85748 Min:      3 Act:   53 Avg:   76 Max:    8148
T: 6 (17769) P: 0 I:4000 C:  75153 Min:      3 Act:   53 Avg:   92 Max:    7510
T: 7 (17770) P: 0 I:4500 C:  66807 Min:      3 Act:   55 Avg:   81 Max:    8709

instance-b, launched w. custom slice, and verifies via live peek with crash.
homer:/root # schedtool -v -s 100000 -e cyclictest -Smq
PID 17753: PRIO   0, POLICY N: SCHED_NORMAL  , NICE   0, EEVDF_NICE   0, EEVDF_SLICE 100000, AFFINITY 0xff
# /dev/cpu_dma_latency set to 0us
T: 0 (17754) P: 0 I:1000 C: 297014 Min:      1 Act:   51 Avg:   79 Max:    9584
T: 1 (17755) P: 0 I:1500 C: 198401 Min:      1 Act: 3845 Avg:  118 Max:    9995
T: 2 (17756) P: 0 I:2000 C: 149137 Min:      1 Act:  103 Avg:  125 Max:    8863
T: 3 (17757) P: 0 I:2500 C: 119519 Min:      1 Act:   52 Avg:  218 Max:    9704
T: 4 (17758) P: 0 I:3000 C:  99760 Min:      1 Act:   51 Avg:  134 Max:   11108
T: 5 (17759) P: 0 I:3500 C:  85731 Min:      1 Act:   53 Avg:  234 Max:    9649
T: 6 (17760) P: 0 I:4000 C:  75321 Min:      2 Act:   53 Avg:  139 Max:    7351
T: 7 (17761) P: 0 I:4500 C:  66929 Min:      3 Act:   51 Avg:  191 Max:    6469
                                                               ^^^ hmm
Those Avg: numbers follow the custom slice.

homer:/root # schedtool -v -s 500000 -e cyclictest -Smq
PID 29755: PRIO   0, POLICY N: SCHED_NORMAL  , NICE   0, EEVDF_NICE   0, EEVDF_SLICE 500000, AFFINITY 0xff
# /dev/cpu_dma_latency set to 0us
T: 0 (29756) P: 0 I:1000 C: 352348 Min:      1 Act:   51 Avg:   67 Max:   10259
T: 1 (29757) P: 0 I:1500 C: 229618 Min:      1 Act:   59 Avg:  121 Max:    8439
T: 2 (29758) P: 0 I:2000 C: 176031 Min:      1 Act:   54 Avg:  159 Max:    8839
T: 3 (29759) P: 0 I:2500 C: 139346 Min:      1 Act:   52 Avg:  186 Max:    9498
T: 4 (29760) P: 0 I:3000 C: 117779 Min:      2 Act:   54 Avg:  172 Max:    8862
T: 5 (29761) P: 0 I:3500 C: 101272 Min:      1 Act:   54 Avg:  180 Max:    9331
T: 6 (29762) P: 0 I:4000 C:  88781 Min:      3 Act:   54 Avg:  208 Max:    7111
T: 7 (29763) P: 0 I:4500 C:  78986 Min:      1 Act:  143 Avg:  168 Max:    6677

homer:/root # cyclictest -Smq
# /dev/cpu_dma_latency set to 0us
T: 0 (29747) P: 0 I:1000 C: 354262 Min:      2 Act:   51 Avg:   65 Max:    9754
T: 1 (29748) P: 0 I:1500 C: 236885 Min:      1 Act:   43 Avg:   56 Max:    8434
T: 2 (29749) P: 0 I:2000 C: 177461 Min:      3 Act:   53 Avg:   75 Max:    9028
T: 3 (29750) P: 0 I:2500 C: 142315 Min:      2 Act:   53 Avg:   74 Max:    7654
T: 4 (29751) P: 0 I:3000 C: 118642 Min:      3 Act:   51 Avg:   78 Max:    8169
T: 5 (29752) P: 0 I:3500 C: 101833 Min:      3 Act:   52 Avg:   75 Max:    7790
T: 6 (29753) P: 0 I:4000 C:  89065 Min:      3 Act:   52 Avg:   76 Max:    8001
T: 7 (29754) P: 0 I:4500 C:  79323 Min:      3 Act:   54 Avg:   78 Max:    7703