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SubjectRe: [PATCH v5] sched: Avoid unnecessary work in reweight_entity
Hi, Peter

I have collected more testing data, here is the test results:

Machine: ThinkPad T420
OS: Ubuntu 11.10
Benchmark: time make -j14 (build kernel)

pre:

real user sys
1. 38m32.274s 111m53.116s 15m31.866s
2. 38m36.775s 110m49.364s 16m40.927s
3. 38m48.107s 111m29.806s 16m35.794s
4. 38m35.009s 111m41.443s 16m9.705s
5 38m49.189s 112m14.973s 15m57.924s
6. 38m34.523s 109m0.265s 17m6.584s
7. 38m38.986s 110m3.385s 16m52.735s

Avg 38m47.838s 111m1.765s 16m25.076s

post:

real user sys
1. 39m32.546s 113m28.918s 16m19.217s
2. 38m40.743s 112m9.057s 15m34.246s
3. 39m12.018s 113m9.192s 16m22.933s
4. 38m55.000s 113m56.203s 15m41.343s
5. 38m53.893s 111m35.814s 15m45.303s
6. 38m48.234s 111m17.537s 15m41.287s
7. 39m11.803s 111m2.760s 16m0.012s

Avg 39m2.034s 112m22.783s 15m50.055s

Summary:
real user sys user + sys
pre Avg 38m47.838s 111m1.765s 16m25.076s 127m26.841s
post Avg 39m2.034s 112m22.783s 15m50.055s 128m12.838s
+0.6% +1.22% -3.69% +0.6%

The machine is dedicated, so I think the results should be accurate,
what we can see is the time cost in sys reduced obviously, I think this
is caused by "reweight_entity"'s reduced execution time(which we can check
in user space).

But I was confused that why the time 'user' and 'real' increased while the
'sys' down, so I really want to know your opinion on the testing result, and
will be appreciate if some one willing to provide his point of view.

Regards,
Michael Wang

On 02/24/2012 10:08 AM, Michael Wang wrote:

> On 02/23/2012 06:40 PM, Michael Wang wrote:
>
>> On 02/20/2012 09:08 PM, Peter Zijlstra wrote:
>>
>> Hi, Peter
>>
>> Sorry for reply so late, I was blocked by some issue army while setup the
>> testing environment.
>>
>>> On Sat, 2012-02-18 at 09:43 +0800, Michael Wang wrote:
>>>> And as reight_entity is invoked very often, I think this patch can do some help to the
>>>> performance, although there are no numbers, we can prove it logically :)
>>>
>>> Well, you're probably right (although I think you completely ignored the
>>> optimizing compiler), but still it would be good to get some numbers to
>>> confirm reality :-)
>>
>>
>> That's right, if consider the compiler's optimization, the logic improvements
>> I listed may not be true...
>>
>>>
>>
>>> Just pick your favourite cgroup workload/benchmark and run a pre/post
>>> comparison, possible using perf record.
>>>
>>> If all squares up you should see an improvement in your benchmark score
>>> as well as see a reduction in time spend in the function you're
>>> patching.
>>
>>
>> So I created a cpuset cgroup 'rg1' and his sub memory group 'sub',
>> attached current shell to 'sub', then use 'time make kernel' as benchmark.
>>
>> Below is the test result:
>>
>> 'time make':
>> old
>> real: 87m53.804s user: 66m41.886s sys: 11m51.792s
>> new
>> real: 86m8.485s user: 65m49.211s sys: 11m47.264s
>>
>> 'time make -j14':
>> old:
>> real: 42m43.825s user: 124m13.726s sys: 17m57.183s
>> new
>> real: 39m0.072s user: 114m33.258s sys: 15m30.662s
>>
>
>
> Hi, Peter
>
> Someone notify me that this result is ridiculous, I should have done more test,
> not just once, this is really my fault, please give me more time, I will back
> with more data so we can use average number.
>
> Regards,
> Michael Wang
>
>> I also try to use 'perf sched record', but I can only record few seconds time,
>> otherwise it will be too big and report some error, as the record time is too
>> short, results are very different from each other, I failed to use them to prove
>> the patch:(
>>
>> I also have try to use some other method, I moved 'reweight_entity' and related
>> functions to user space, and invoke it 10000000 times in 'main', I have append
>> part of the code (really raw...) in the end.
>>
>> Three times output is:
>>
>> old:
>> real 0m0.715s 0m0.710s 0m0.739s
>> user 0m0.716s 0m0.708s 0m0.736s
>> sys 0m0.000s 0m0.000s 0m0.000s
>>
>> new:
>> real 0m0.318s 0m0.308s 0m0.317s
>> user 0m0.316s 0m0.304s 0m0.316s
>> sys 0m0.000s 0m0.000s 0m0.000s
>>
>> It seems like that new code can save more then half execution time, but also we
>> can see, after calculation, what I have done can only save 0.04ns(too small...).
>>
>> The user space test result is not accurate but at least we can know new code is
>> faster then old.
>>
>> Please tell me if we need to do some thing else, and thanks for your suggestion :)
>>
>> Regards,
>> Michael Wang
>>
>>
>>
>> User space code:
>>
>> void
>> account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>> {
>> update_load_add(&cfs_rq->load, se->load.weight);
>> if (1)
>> update_load_add(&cfs_rq->load, se->load.weight);
>> if (1) {
>> add_cfs_task_weight(cfs_rq, se->load.weight);
>> list_add(&se->group_node, &cfs_rq->tasks);
>> }
>> cfs_rq->nr_running++;
>> }
>>
>> void
>> account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>> {
>> update_load_sub(&cfs_rq->load, se->load.weight);
>> if (1)
>> update_load_sub(&cfs_rq->load, se->load.weight);
>> if (1) {
>> add_cfs_task_weight(cfs_rq, -se->load.weight);
>> list_del_init(&se->group_node);
>> }
>> cfs_rq->nr_running--;
>> }
>>
>> void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>> unsigned long weight)
>> {
>> if (1) {
>> account_entity_dequeue(cfs_rq, se);
>> }
>>
>> update_load_set(&se->load, weight);
>>
>> if (1)
>> account_entity_enqueue(cfs_rq, se);
>> }
>>
>> void reweight_entity_new(struct cfs_rq *cfs_rq, struct sched_entity *se,
>> unsigned long weight)
>> {
>> if (1) {
>> update_load_add(&cfs_rq->load, weight - se->load.weight);
>> if(1)
>> update_load_add(&cfs_rq->load, weight -
>> se->load.weight);
>> if(1)
>> add_cfs_task_weight(cfs_rq, weight
>> -se->load.weight);
>> }
>> update_load_set(&se->load, weight);
>> }
>>
>> int main()
>> {
>> struct cfs_rq cfsrq;
>> struct sched_entity se;
>> memset(&cfsrq, 0, sizeof(struct cfs_rq));
>> memset(&se, 0, sizeof(struct sched_entity));
>> INIT_LIST_HEAD(&se.group_node);
>> INIT_LIST_HEAD(&cfsrq.tasks);
>> int i = 10000000;
>> while(i) {
>> i--;
>> reweight_entity_new(&cfsrq, &se, 10);
>> //reweight_entity(&cfsrq, &se, 10);
>> }
>> }
>>
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>>
>>
>>
>>
>>
>>
>>
>>
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>
>
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