Re: [PATCH v3] sched/fair: Introduce SIS_UTIL to search idle CPU based on sum of util_avg

[Yicong Yang <yangyicong@huawei.com>]

On 2022/5/12 16:14, Chen Yu wrote:
> On Tue, May 10, 2022 at 08:41:57PM +0800, Yicong Yang wrote:
>> On 2022/4/29 2:24, Chen Yu wrote:
>>> @@ -61,6 +61,7 @@ SCHED_FEAT(TTWU_QUEUE, true)
>>>   * When doing wakeups, attempt to limit superfluous scans of the LLC domain.
>>>   */
>>>  SCHED_FEAT(SIS_PROP, true)
>>> +SCHED_FEAT(SIS_UTIL, false)
>>>  
>>
>> I see you mentioned they're mutually exclusive in the commit, worth a comment here?
>>
> Yes, previously I thought it could be made mutually exclusive, and Peter has
> suggested that we should make SIS_UTIL enabled by default, so later we could
> remove SIS_PROP if SIS_UTIL behaves stable. So I assume there is no need to
> add comment in the next version now. 
>> One minor question: nr is updated in load balance so there maybe a delay because of
>> interval of load balancing.
> Yes, this is a good question. The default interval between two load balance is sd_weight ms,
> which is 112ms in my case. This interval was a trade off to reduce cache contention. Besides,
> every 1st idle CPU or the balanced CPU in one sched group within the LLC domain has the chance
> to launch a periodic load balance, for example, although CPU0 and CPU1's periodic load balance
> are both triggered every 112ms, CPU1 could help launch the load balance when CPU0 is not in
> load balance work. Consider there are many CPUs in a LLC domain, the 'internal' to launch
> the periodic load balance becomes smaller.
>> Furthermore, the LLC domain may not be balanced everytime
>> if the lowest domain is not LLC, like CLS->LLC. So maybe a bit more delay included.
>>
> I thought every domain has its chance to launch a load balance, the difference is different
> domains have different interval. No?
I might miss something. I think it's right here.
>> The test results is fine and as expected. The improvement of netperf at a heavy load
>> condition, compared to your v2 version.
>>
> Thanks for the test, would you mind if I add Tested-by tag?
> 

On Kunpeng920 for this patch,

Tested-by: Yicong Yang <yangyicong@hisilicon.com>

> thanks,
> Chenyu 
>> Thanks,
>> Yicong
>>
>> TCP_RR node 0-1
>> threads
>> 16	57559.56667	57930.03333 (+0.64%)
>> 32	56373		57754.53333 (+2.45%)
>> 64	18831.4		46234.76667 (+145.52%)
>> 128	15658.9		19620.26667 (+25.30%)
>> 256	7959.896667	8869.013333 (+11.42%)
>>
>> TCP_RR node 0
>> threads
>> 16	58389.43333	59026.03333 (+1.09%)
>> 32	23779.6		51563.33333 (+116.84%)
>> 64	20514.56667	23485.63333 (+14.48%)
>> 128	8202.49		9205.483333 (+12.23%)
>> 256	3843.163333	4304.8      (+12.01%)
>>
>> tbench4 node 0-1
>>                            5.18-rc1                patched
>> Hmean     1        299.02 (   0.00%)      307.73 *   2.91%*
>> Hmean     2        597.88 (   0.00%)      619.10 *   3.55%*
>> Hmean     4       1207.11 (   0.00%)     1239.57 *   2.69%*
>> Hmean     8       2406.67 (   0.00%)     2463.63 *   2.37%*
>> Hmean     16      4755.52 (   0.00%)     4979.46 *   4.71%*
>> Hmean     32      9449.01 (   0.00%)     9709.59 *   2.76%*
>> Hmean     64     10538.89 (   0.00%)    10727.86 *   1.79%*
>> Hmean     128    13333.84 (   0.00%)    14580.63 *   9.35%*
>> Hmean     256    11735.24 (   0.00%)    11737.16 (   0.02%)
>>
>> tbench4 node 0
>>                            5.18-rc1                patched
>> Hmean     1        302.26 (   0.00%)      313.43 *   3.70%*
>> Hmean     2        603.87 (   0.00%)      618.56 *   2.43%*
>> Hmean     4       1213.91 (   0.00%)     1249.63 *   2.94%*
>> Hmean     8       2469.72 (   0.00%)     2527.48 *   2.34%*
>> Hmean     16      4980.70 (   0.00%)     5099.62 *   2.39%*
>> Hmean     32      9001.88 (   0.00%)     9730.27 *   8.09%*
>> Hmean     64      7032.07 (   0.00%)     7691.56 *   9.38%*
>> Hmean     128     6037.76 (   0.00%)     6712.86 *  11.18%*
>> Hmean     256     8513.83 (   0.00%)     9117.79 *   7.09%*
>>
> .
>