On Thu, Aug 03, 2023 at 10:53:24AM +0200, Claudio Jeker wrote:
> On Thu, Aug 03, 2023 at 10:13:57AM +0200, Martin Pieuchot wrote:
> > On 02/08/23(Wed) 14:22, Claudio Jeker wrote:
> > > On Mon, Jul 31, 2023 at 10:21:11AM -0500, Scott Cheloha wrote:
> > > > On Fri, Jul 28, 2023 at 07:36:41PM -0500, Scott Cheloha wrote:
> > > > > claudio@ notes that uvm_loadav() pointlessly walks the allproc list to
> > > > > recompute schedstate_percpu.spn_nrun for each CPU.
> > > > >
> > > > > We can just use the value instead of recomputing it.
> > > >
> > > > Whoops, off-by-one. The current load averaging code includes the
> > > > running thread in the nrun count if it is *not* the idle thread.
> > >
> > > Yes, with this the loadavg seems to be consistent and following the number
> > > of running processes. The code seems to behave like before (with all its
> > > quirks).
> > >
> > > OK claudio@, this is a good first step. Now I think this code should later
> > > be moved into kern_sched.c or sched_bsd.c and removed from uvm. Not sure
> > > why
> > > the load calculation is part of memory management...
> > >
> > > On top of this I wonder about the per-CPU load calculation. In my opinion
> > > it is wrong to skip the calculation if the CPU is idle. Because of this
> > > there is no decay for idle CPUs and that feels wrong to me.
> > > Do we have a userland utility that reports spc_ldavg?
> >
> > I don't understand why the SCHED_LOCK() is needed. Since I'm really
> > against adding new uses for it, could you comment on that?
>
> The question is how sloppy do we want to be. This code looks at
> ci_schedstate (spc_idleproc and spc_nrun) and ci_curproc so the be correct
> this needs to lock the scheduler. Do we really want that, hell no.
How about this. Kill the spc_ldavg calculation. Its use is more then
questionable. The cpu selection code using this is not wroking well and
process stealing will do the rest.
Also use sched_cpu_idle to know if a cpu is idle.
--
:wq Claudio
Index: kern/kern_sched.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_sched.c,v
retrieving revision 1.81
diff -u -p -r1.81 kern_sched.c
--- kern/kern_sched.c 27 Jul 2023 17:52:53 -0000 1.81
+++ kern/kern_sched.c 3 Aug 2023 08:41:38 -0000
@@ -373,7 +373,6 @@ sched_choosecpu_fork(struct proc *parent
{
#ifdef MULTIPROCESSOR
struct cpu_info *choice = NULL;
- fixpt_t load, best_load = ~0;
int run, best_run = INT_MAX;
struct cpu_info *ci;
struct cpuset set;
@@ -407,13 +406,10 @@ sched_choosecpu_fork(struct proc *parent
while ((ci = cpuset_first(&set)) != NULL) {
cpuset_del(&set, ci);
- load = ci->ci_schedstate.spc_ldavg;
run = ci->ci_schedstate.spc_nrun;
- if (choice == NULL || run < best_run ||
- (run == best_run &&load < best_load)) {
+ if (choice == NULL || run < best_run) {
choice = ci;
- best_load = load;
best_run = run;
}
}
@@ -605,11 +601,6 @@ sched_proc_to_cpu_cost(struct cpu_info *
*/
if (CPU_IS_PRIMARY(ci))
cost += sched_cost_runnable;
-
- /*
- * Higher load on the destination means we don't want to go there.
- */
- cost += ((sched_cost_load * spc->spc_ldavg) >> FSHIFT);
/*
* If the proc is on this cpu already, lower the cost by how much
Index: sys/sched.h
===================================================================
RCS file: /cvs/src/sys/sys/sched.h,v
retrieving revision 1.58
diff -u -p -r1.58 sched.h
--- sys/sched.h 25 Jul 2023 18:16:19 -0000 1.58
+++ sys/sched.h 3 Aug 2023 08:42:39 -0000
@@ -110,7 +110,6 @@ struct schedstate_percpu {
struct clockintr *spc_profclock; /* [o] profclock handle */
u_int spc_nrun; /* procs on the run queues */
- fixpt_t spc_ldavg; /* shortest load avg. for this cpu */
volatile uint32_t spc_whichqs;
volatile u_int spc_spinning; /* this cpu is currently spinning */
Index: uvm/uvm_meter.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_meter.c,v
retrieving revision 1.46
diff -u -p -r1.46 uvm_meter.c
--- uvm/uvm_meter.c 2 Aug 2023 13:54:45 -0000 1.46
+++ uvm/uvm_meter.c 3 Aug 2023 10:12:02 -0000
@@ -70,7 +70,7 @@ struct loadavg averunnable;
* 5 second intervals.
*/
-static fixpt_t cexp[3] = {
+static const fixpt_t cexp[3] = {
0.9200444146293232 * FSCALE, /* exp(-1/12) */
0.9834714538216174 * FSCALE, /* exp(-1/60) */
0.9944598480048967 * FSCALE, /* exp(-1/180) */
@@ -98,27 +98,16 @@ uvm_meter(void)
static void
uvm_loadav(struct loadavg *avg)
{
+ extern struct cpuset sched_idle_cpus;
CPU_INFO_ITERATOR cii;
struct cpu_info *ci;
- struct schedstate_percpu *spc;
- u_int i, nrun = 0, nrun_cpu;
- int s;
+ u_int i, nrun = 0;
-
- SCHED_LOCK(s);
CPU_INFO_FOREACH(cii, ci) {
- spc = &ci->ci_schedstate;
- nrun_cpu = spc->spc_nrun;
- if (ci->ci_curproc != spc->spc_idleproc)
- nrun_cpu++;
- if (nrun_cpu == 0)
- continue;
- spc->spc_ldavg = (cexp[0] * spc->spc_ldavg +
- nrun_cpu * FSCALE *
- (FSCALE - cexp[0])) >> FSHIFT;
- nrun += nrun_cpu;
+ if (!cpuset_isset(&sched_idle_cpus, ci))
+ nrun++;
+ nrun += ci->ci_schedstate.spc_nrun;
}
- SCHED_UNLOCK(s);
for (i = 0; i < 3; i++) {
avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
