Re: [PATCH] psi: reduce calls to sched_clock() in psi

[Johannes Weiner]

On Sun, Mar 21, 2021 at 01:51:56PM -0700, Shakeel Butt wrote:
> We noticed that the cost of psi increases with the increase in the
> levels of the cgroups. Particularly the cost of cpu_clock() sticks out
> as the kernel calls it multiple times as it traverses up the cgroup
> tree. This patch reduces the calls to cpu_clock().
> 
> Performed perf bench on Intel Broadwell with 3 levels of cgroup.
> 
> Before the patch:
> 
> $ perf bench sched all
>  # Running sched/messaging benchmark...
>  # 20 sender and receiver processes per group
>  # 10 groups == 400 processes run
> 
>      Total time: 0.747 [sec]
> 
>  # Running sched/pipe benchmark...
>  # Executed 1000000 pipe operations between two processes
> 
>      Total time: 3.516 [sec]
> 
>        3.516689 usecs/op
>          284358 ops/sec
> 
> After the patch:
> 
> $ perf bench sched all
>  # Running sched/messaging benchmark...
>  # 20 sender and receiver processes per group
>  # 10 groups == 400 processes run
> 
>      Total time: 0.640 [sec]
> 
>  # Running sched/pipe benchmark...
>  # Executed 1000000 pipe operations between two processes
> 
>      Total time: 3.329 [sec]
> 
>        3.329820 usecs/op
>          300316 ops/sec
> 
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>