Re: [External] : Re: [LKP] Re: [locking/qspinlock] 0e8d8f4f12: stress-ng.zero.ops_per_sec -9.7% regression

[Alex Kogan]

> On Mar 22, 2021, at 7:15 PM, Alex Kogan <alex.kogan@xxxxxxxxxx> wrote:
> 
> Many thanks to Zhengjun Xing for the help in reproducing the issue.
> 
> On our system, the regression is less than 7% (the numbers are below), however,
> at least at the full capacity, the numbers are very stable. This allowed me to track down the
> issue and identify unnecessary stores into the queue node structure, which may cause 
> cache misses during lock transfers. Moving those stores into the initialization code (cna_init_nodes())
> solves the problem.
> 
> Below are the numbers of “bogo ops/s” reported by stress-ng with various numbers of workers. 
> Each number represents an average over 25 runs, with the standard deviation reported in ().
> 
> #workers      stock                          CNA / speedup               CNA+patch / speedup
>  18  16327.844 (581.744) 15480.061 (582.654) / 0.948  16422.349 (473.729) / 1.006
>  36    8573.557 (285.058)   8003.888 (196.125) / 0.934    8457.436 (258.065) / 0.986
>  72    4042.535 (28.766)     3960.407 (28.648) / 0.980      4107.143 (23.037) / 1.016
> 108   2735.913 (7.440)       2678.888 (7.102) / 0.979        2774.751 (4.375) / 1.014
> 144   2093.477 (3.341)       2042.968 (1.982) / 0.976        2109.879 (1.714) / 1.008

Those are "bogo ops/s (usr+sys time)", btw. Just in case, below are "bogo ops/s (real time)”
numbers, which I believe is what is reported by the kernel test robot:

#workers      stock                     CNA / speedup               CNA+patch / speedup
 18   262932.282 (12638.248)   249653.081 (11822.940) / 0.949  265189.104 (9271.447) / 1.009
 36   277315.640 (11100.324)   260177.335 (7186.451) / 0.938   274691.250 (10329.523) / 0.991
 72   263904.000 (2128.206)    259967.180 (1857.393) / 0.985   268971.483 (1713.639) / 1.019
108   273811.373 (664.517)     268949.947 (690.329) / 0.982    278196.867 (403.978) / 1.016
144   284321.364 (399.281)     278153.208 (210.776) / 0.978    287343.806 (280.963) / 1.011

Regards,
— Alex

> The patch is attached. As always, comments are welcome!
> 
> Unless there any objections, I will reintegrate the patch into the series, and post a new
> revision.
> 
> Regards,
> — Alex