Re: [RFC next v2 0/5] ucount: add rlimit cache for ucount

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2025-05-09 13:18:49 [-0700], Andrew Morton wrote:
> On Fri,  9 May 2025 07:20:49 +0000 Chen Ridong <chenridong@huaweicloud.com> wrote:
> 
> > The will-it-scale test case signal1 [1] has been observed. and the test
> > results reveal that the signal sending system call lacks linearity.
> > To further investigate this issue, we initiated a series of tests by
> > launching varying numbers of dockers and closely monitored the throughput
> > of each individual docker. The detailed test outcomes are presented as
> > follows:
> > 
> > 	| Dockers     |1      |4      |8      |16     |32     |64     |
> > 	| Throughput  |380068 |353204 |308948 |306453 |180659 |129152 |
> > 
> > The data clearly demonstrates a discernible trend: as the quantity of
> > dockers increases, the throughput per container progressively declines.
> > In-depth analysis has identified the root cause of this performance
> > degradation. The ucouts module conducts statistics on rlimit, which
> > involves a significant number of atomic operations. These atomic
> > operations, when acting on the same variable, trigger a substantial number
> > of cache misses or remote accesses, ultimately resulting in a drop in
> > performance.
> 
> Did you consider simply turning that atomic_t counter into a
> percpu_counter?

That sounds like a smaller change. Also, do these 1…64 docker container
play signal ping-pong or is there a real workload behind it?

Sebastian