Re: [PATCH] sched/fair: Optimize select_idle_cpu

[chengjian (D)]

On 2019/12/12 22:41, Cheng Jian wrote:
> Our threads are all bind to the front CPUs of the LLC domain,
> and now all the threads runs on the last CPU of them. nr is
> always less than the cpumask_weight, for_each_cpu_wrap can't
> find the CPU which our threads can run on, so the threads stay
> at the last CPU all the time.
Test :

Run on ARM64 4NODE, 128 CORE

// cat a.c
#include <time.h>

int main(void)
{
ÂÂÂ struct timespec time, save;
ÂÂÂ int ret;

ÂÂÂ time.tv_sec = 0;
ÂÂÂ time.tv_nsec = 1;

ÂÂÂ while (1) {
ÂÂÂÂÂÂÂ ret = nanosleep(&time, &save);
ÂÂÂÂÂÂÂ if (ret)
ÂÂÂÂÂÂÂÂÂÂÂ nanosleep(&save, &save);
ÂÂÂ }
ÂÂÂ return 0;
}

#cat a.sh
for i in `seq 0 9`
do
ÂÂÂ taskset -c 8-11 ./a.out &
done


then run:

ÂÂÂ gcc a.c -o a.out
ÂÂÂ sh a.sh



without this patch, you can see all the task run on CPU11 all the times.



 %Cpu8 : 0.0 us, 0.0 sy, 0.0 ni, 98.4 id, 0.0 wa, 1.6 hi, 0.0 
si, 0.0 st
 %Cpu9 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 
si, 0.0 st
 %Cpu10 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 
si, 0.0 st
 %Cpu11 : 5.7 us, 40.0 sy, 0.0 ni, 45.7 id, 0.0 wa, 8.6 hi, 0.0 
si, 0.0 st