On 25/01/19(Fri) 02:24, Alexander Bluhm wrote:
> 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.
In that case I'd like to commit it without the "#ifdef chunk". Stop
accounting/updating priorities of Idle threads. Ok?
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 26 Jan 2019 16:26:08 -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 26 Jan 2019 16:26:22 -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 +535,12 @@ 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)
+ return;
SCHED_LOCK(s);
p->p_estcpu = ESTCPULIM(p->p_estcpu + 1);
