On Tue, Jan 22, 2019 at 12:19:11PM -0200, Martin Pieuchot wrote:
> > There are still things I don't understand. After a while the CPU
> > time for idle5, idle6, idle7 does not increase anymore. I am doing
> > iperf3 performance tests on this machine. My patch makes the results
> > more unsteady and throughput lower. It seems that iperf3 processes
> > get scheduled on CPUs with less memory affinity.
>
> What do you mean with CPU time?
The TIME reported in ps or top for a process. For idle threads on
idle CPUs it is not reported corrrectly. There needs to be a real
process scheduled on this core for updating the time.
> Since you're doing tests, could you try the diff below? It stops
> recalculating the priority of Idle threads. The first effect is fewer
> contention on the SCHED_LOCK() and it also implicitly document the
> current fun :)
This diff works as expected, CPU percentage of idle thread is now
0%.
> I left an "#if 0" below. You could try enabling it. Does it change
> anything? I hope not.
Same behavior with #if 1.
bluhm
> Index: kern/kern_clock.c
> ===================================================================
> RCS file: /cvs/src/sys/kern/kern_clock.c,v
> retrieving revision 1.97
> diff -u -p -r1.97 kern_clock.c
> --- kern/kern_clock.c 17 Oct 2018 12:25:38 -0000 1.97
> +++ kern/kern_clock.c 22 Jan 2019 13:07:25 -0000
> @@ -400,8 +400,7 @@ statclock(struct clockframe *frame)
> * ~~16 Hz is best
> */
> if (schedhz == 0) {
> - if ((++curcpu()->ci_schedstate.spc_schedticks & 3) ==
> - 0)
> + if ((++spc->spc_schedticks & 3) == 0)
> schedclock(p);
> }
> }
> Index: kern/sched_bsd.c
> ===================================================================
> RCS file: /cvs/src/sys/kern/sched_bsd.c,v
> retrieving revision 1.48
> diff -u -p -r1.48 sched_bsd.c
> --- kern/sched_bsd.c 6 Jan 2019 12:59:45 -0000 1.48
> +++ kern/sched_bsd.c 22 Jan 2019 14:15:28 -0000
> @@ -218,6 +218,13 @@ schedcpu(void *arg)
>
> LIST_FOREACH(p, &allproc, p_list) {
> /*
> + * Idle threads are never placed in runqueue, therefore
> + * computing their priority is pointless.
> + */
> + if (p->p_cpu != NULL &&
> + p->p_cpu->ci_schedstate.spc_idleproc == p)
> + continue;
> + /*
> * Increment sleep time (if sleeping). We ignore overflow.
> */
> if (p->p_stat == SSLEEP || p->p_stat == SSTOP)
> @@ -528,7 +535,17 @@ resetpriority(struct proc *p)
> void
> schedclock(struct proc *p)
> {
> + struct cpu_info *ci = curcpu();
> + struct schedstate_percpu *spc = &ci->ci_schedstate;
> int s;
> +
> + if (p == spc->spc_idleproc) {
> +#if 0
> + if (spc->spc_nrun)
> + need_resched(ci);
> +#endif
> + return;
> + }
>
> SCHED_LOCK(s);
> p->p_estcpu = ESTCPULIM(p->p_estcpu + 1);
