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SubjectRe: Bench for testing scheduler
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On 8 November 2013 01:04, Rowand, Frank <Frank.Rowand@sonymobile.com> wrote:
> Hi Vincent,
>
> Thanks for creating some benchmark numbers!

you're welcome

>
>
> On Thursday, November 07, 2013 5:33 AM, Vincent Guittot [vincent.guittot@linaro.org] wrote:
>>
>> On 7 November 2013 12:32, Catalin Marinas <catalin.marinas@arm.com> wrote:
>> > Hi Vincent,
>> >
>> > (for whatever reason, the text is wrapped and results hard to read)
>>
>> Yes, i have just seen that. It looks like gmail has wrapped the lines.
>> I have added the results which should not be wrapped, at the end of this email
>>
>> >
>> >
>> > On Thu, Nov 07, 2013 at 10:54:30AM +0000, Vincent Guittot wrote:
>> >> During the Energy-aware scheduling mini-summit, we spoke about benches
>> >> that should be used to evaluate the modifications of the scheduler.
>> >> I’d like to propose a bench that uses cyclictest to measure the wake
>> >> up latency and the power consumption. The goal of this bench is to
>> >> exercise the scheduler with various sleeping period and get the
>> >> average wakeup latency. The range of the sleeping period must cover
>> >> all residency times of the idle state table of the platform. I have
>> >> run such tests on a tc2 platform with the packing tasks patchset.
>> >> I have use the following command:
>> >> #cyclictest -t <number of cores> -q -e 10000000 -i <500-12000> -d 150 -l 2000
>
> The number of loops ("-l 2000") should be much larger to create useful
> results. I don't have a specific number that is large enough, I just
> know from experience that 2000 is way too small. For example, running
> cyclictest several times with the same values on my laptop gives values
> that are not consistent:

The Avg figures look almost stable IMO. Are you speaking about the Max
value for the inconsistency ?

>
> $ sudo ./cyclictest -t -q -e 10000000 -i 500 -d 150 -l 2000
> # /dev/cpu_dma_latency set to 10000000us
> T: 0 ( 9703) P: 0 I:500 C: 2000 Min: 2 Act: 90 Avg: 77 Max: 243
> T: 1 ( 9704) P: 0 I:650 C: 1557 Min: 2 Act: 58 Avg: 68 Max: 226
> T: 2 ( 9705) P: 0 I:800 C: 1264 Min: 2 Act: 54 Avg: 81 Max: 1017
> T: 3 ( 9706) P: 0 I:950 C: 1065 Min: 2 Act: 11 Avg: 80 Max: 260
>
> $ sudo ./cyclictest -t -q -e 10000000 -i 500 -d 150 -l 2000
> # /dev/cpu_dma_latency set to 10000000us
> T: 0 ( 9709) P: 0 I:500 C: 2000 Min: 2 Act: 45 Avg: 74 Max: 390
> T: 1 ( 9710) P: 0 I:650 C: 1554 Min: 2 Act: 82 Avg: 61 Max: 810
> T: 2 ( 9711) P: 0 I:800 C: 1263 Min: 2 Act: 83 Avg: 74 Max: 287
> T: 3 ( 9712) P: 0 I:950 C: 1064 Min: 2 Act: 103 Avg: 79 Max: 551
>
> $ sudo ./cyclictest -t -q -e 10000000 -i 500 -d 150 -l 2000
> # /dev/cpu_dma_latency set to 10000000us
> T: 0 ( 9716) P: 0 I:500 C: 2000 Min: 2 Act: 82 Avg: 72 Max: 252
> T: 1 ( 9717) P: 0 I:650 C: 1556 Min: 2 Act: 115 Avg: 77 Max: 354
> T: 2 ( 9718) P: 0 I:800 C: 1264 Min: 2 Act: 59 Avg: 78 Max: 1143
> T: 3 ( 9719) P: 0 I:950 C: 1065 Min: 2 Act: 104 Avg: 70 Max: 238
>
> $ sudo ./cyclictest -t -q -e 10000000 -i 500 -d 150 -l 2000
> # /dev/cpu_dma_latency set to 10000000us
> T: 0 ( 9722) P: 0 I:500 C: 2000 Min: 2 Act: 82 Avg: 68 Max: 213
> T: 1 ( 9723) P: 0 I:650 C: 1555 Min: 2 Act: 65 Avg: 65 Max: 1279
> T: 2 ( 9724) P: 0 I:800 C: 1264 Min: 2 Act: 91 Avg: 69 Max: 244
> T: 3 ( 9725) P: 0 I:950 C: 1065 Min: 2 Act: 58 Avg: 76 Max: 242
>
>
>> >
>> > cyclictest could be a good starting point but we need to improve it to
>> > allow threads of different loads, possibly starting multiple processes
>> > (can be done with a script), randomly varying load threads. These
>> > parameters should be loaded from a file so that we can have multiple
>> > configurations (per SoC and per use-case). But the big risk is that we
>> > try to optimise the scheduler for something which is not realistic.
>>
>> The goal of this simple bench is to measure the wake up latency and the reachable value of the scheduler on a platform but not to emulate a "real" use case. In the same way than sched-pipe tests a specific behavior of the scheduler, this bench tests the wake up latency of a system.
>>
>> Starting multi processes and adding some loads can also be useful but the target will be a bit different from wake up latency. I have one concern with randomness because it prevents from having repeatable and comparable tests and results.
>>
>> I agree that we have to test "real" use cases but it doesn't prevent from testing the limit of a characteristic on a system
>>
>> >
>> >
>> > We are working on describing some basic scenarios (plain English for
>> > now) and one of them could be video playing with threads for audio and
>> > video decoding with random change in the workload.
>> >
>> > So I think the first step should be a set of tools/scripts to analyse
>> > the scheduler behaviour, both in terms of latency and power, and these
>> > can use perf sched. We can then run some real life scenarios (e.g.
>> > Android video playback) and build a benchmark that matches such
>> > behaviour as close as possible. We can probably use (or improve) perf
>> > sched replay to also simulate such workload (we may need additional
>> > features like thread dependencies).
>> >
>> >> The figures below give the average wakeup latency and power
>> >> consumption for default scheduler behavior, packing tasks at cluster
>> >> level and packing tasks at core level. We can see both wakeup latency
>> >> and power consumption variation. The detailed result is not a simple
>> >> single value which makes comparison not so easy but the average of all
>> >> measurements should give us a usable “score”.
>> >
>> > How did you assess the power/energy?
>>
>> I have use the embedded joule meter of the tc2.
>>
>> >
>> > Thanks.
>> >
>> > --
>> > Catalin
>>
>> | Default average results | Cluster Packing average results | Core Packing average results
>> | Latency stddev A7 energy A15 energy | Latency stddev A7 energy A15 energy | Latency stddev A7 energy A15 energy
>> | (us) (J) (J) | (us) (J) (J) | (us) (J) (J)
>> | 879 794890 2364175 | 416 879688 12750 | 189 897452 30052
>>
>> Cyclictest | Default | Packing at Cluster level | Packing at Core level
>> Interval | Latency stddev A7 energy A15 energy | Latency stddev A7 energy A15 energy | Latency stddev A7 energy A15 energy
>> (us) | (us) (J) (J) | (us) (J) (J) | (us) (J) (J)
>> 500 24 1 1147477 2479576 21 1 1136768 11693 22 1 1126062 30138
>> 700 22 1 1136084 3058419 21 0 1125280 11761 21 1 1109950 23503
>
> < snip >
>
> Some questions about what these metrics are:
>
> The cyclictest data is reported per thread. How did you combine the per thread data
> to get a single latency and stddev value?
>
> Is "Latency" the average latency?

Yes. I have described below the procedure i have followed to get my results:

I run the same test (same parameters) several times ( i have tried
between 5 and 10 runs and the results were similar).
For each run, i compute the average of per thread average figure and i
compute the stddev between per thread results.
The results that i sent is an average of all runs with the same parameters.

>
> stddev is not reported by cyclictest. How did you create this value? Did you
> use the "-v" cyclictest option to report detailed data, then calculate stddev from
> the detailed data?

No i haven't used the -v because it generates too much spurious wake
up that makes the results irrelevant

Vincent
>
> Thanks,
>
> -Frank
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