Re: Steal time accounting in KVM. Benchmark.

[Alexey Makhalov]

'echo NO_NONTASK_CAPACITY > /sys/kernel/debug/sched_features'  in both guests.
Results:
VM1: STA is disabled -- no changes, still little bit bellow expected 90%
VM2: STA is enabled -- result is changed, but still bad. Hard to say
better or worse. It prefers to stuck at quarters (100% 75% 50% 25%)
Output is attached.

Thanks,
Alexey

On Tue, Oct 20, 2015 at 5:39 AM, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
> Cc Peterz,
> 2015-10-20 5:58 GMT+08:00 Alexey Makhalov <makhaloff@xxxxxxxxx>:
>>
>> Hi,
>>
>> I did benchmarking of scheduler fairness with enabled steal time
>> accounting(STA) in KVM.
>> And results are really interesting.
>>
>> Looks like STA provides worse scheduler fairness against disabled STA
>> (no-steal-acc cmdline param)
>>
>> I created benchmark, main idea is: 2 cgroups with cpu.shares
>> proportion like 1/9, run identical work in both groups, and expecting
>> to get the same proportion of work done â 1/9. Condition â CPU
>> overcommit.
>>
>> On bare metal it is fair +- some percentages of fluctation.
>> On KVM with no STA   itâs less fair. With STA enabled results are
>> ugly! One again â in CPU overcommit situation.
>>
>>
>> Host: ubuntu 14.04, Intel i5 â 2x2 CPUs
>> 2 VMs (4 vCPU each) are working in parallel.   2:1 cpu overcommit.
>>
>> Each VM has running benchmark:
>> cgroups cpu.shares proportion is 128/1152 (10%/90%), work â spinning
>> in cycle, number of cycles are being counted.
>
>
> Could you try if 'echo NO_NONTASK_CAPACITY >
> /sys/kernel/debug/sched_features' in guests works?
>
> Regards,
> Wanpeng Li
90% 28539
75% 31907
76% 30348
75% 43677
75% 29765
63% 30351
74% 28535
70% 29590
65% 31281
87% 29476
75% 29505
75% 29737
75% 29534
75% 29627
89% 30411
75% 29069
74% 29786
74% 29776
74% 29633
74% 29470
74% 29406
90% 30274
90% 29615
96% 30497
100% 29263
100% 29241
100% 29748
100% 29790
99% 29769
74% 66239
52% 118436
50% 117409
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50% 118990
50% 38479
48% 29641
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51% 30109
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49% 29621
49% 29579
43% 80183
49% 118185
49% 113732
45% 29698
25% 29528
24% 30078
36% 29716
32% 28976
43% 77606
19% 131592
0% 39503
12% 29709
25% 29717
24% 29720
25% 29695
25% 29703
25% 29570
25% 29492
25% 29790
25% 29677
25% 29451
25% 29536
25% 29476
25% 29613
24% 30045
24% 30227
37% 52553
43% 29986
50% 29741
49% 30003
50% 29982
35% 29907
39% 30156
48% 30590
66% 58939
--- benchmark was stopped on the first VM. VM1 was in idle from here ---  
90% 58977
89% 58952
90% 58945
89% 58945
90% 58948
89% 59001
89% 58966
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89% 58601
90% 58385
90% 59003
89% 57695
90% 58843
89% 59104
90% 59006
90% 57110
--- to here ---
97% 30300
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100% 28467
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100% 29308
99% 30625
95% 29907
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100% 29626
100% 30054
100% 29744
100% 29693
100% 30008
100% 29935
100% 29825
100% 29684
100% 30010
100% 30163
93% 51597
89% 58972
89% 58692
90% 57975
100% 27946
100% 29624
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75% 29759
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72% 28898
75% 26530
74% 30075
73% 29182
74% 28506
73% 28135
74% 29083
75% 29609
73% 27956
74% 28921
74% 29045
74% 29576
74% 29228
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73% 27872
74% 29787
74% 29633
68% 32062
98% 31992
98% 32120
90% 32984
98% 32568
98% 32307
97% 32300
98% 32262
99% 30436
94% 30023
96% 32511
99% 31075
99% 30112
100% 29835
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100% 29954
100% 29771
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100% 29871
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100% 30807
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99% 30988
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100% 39608