On Fri, 21 Dec 2001, Luigi Rizzo wrote:
> Don't know how interesting this can be, but i am writing
> (no plans to commit it, unless people find it interesting)
> some code to implement a weight-based instead of priority-based
> scheduler. The code is basically the WF2Q+ scheme which is
> already part of dummynet, adapted to processes.
> It is quite compact, and i think i can make it reasonably
> compatible with the old scheme, i.e. a sysctl var can be
> used to switch between one and the other with reasonably
> little overhead.
>
> This would help removing the ugly property that priority-based
> have, which is that one process can starve the rest of the system.
Only broken priority-based schedulers have that property. One of
my incomplete fixes uses weights:
Index: kern_synch.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/kern_synch.c,v
retrieving revision 1.167
diff -u -2 -r1.167 kern_synch.c
--- kern_synch.c 18 Dec 2001 00:27:17 -0000 1.167
+++ kern_synch.c 19 Dec 2001 16:01:26 -0000
@@ -936,18 +1058,18 @@
struct thread *td;
{
- struct kse *ke = td->td_kse;
- struct ksegrp *kg = td->td_ksegrp;
+ struct ksegrp *kg;
- if (td) {
- ke->ke_cpticks++;
- kg->kg_estcpu = ESTCPULIM(kg->kg_estcpu + 1);
- if ((kg->kg_estcpu % INVERSE_ESTCPU_WEIGHT) == 0) {
- resetpriority(td->td_ksegrp);
- if (kg->kg_pri.pri_level >= PUSER)
- kg->kg_pri.pri_level = kg->kg_pri.pri_user;
- }
- } else {
+ if (td == NULL)
panic("schedclock");
- }
+ td->td_kse->ke_cpticks++;
+ kg = td->td_ksegrp;
+#ifdef NEW_SCHED
+ kg->kg_estcpu += niceweights[kg->kg_nice - PRIO_MIN];
+#else
+ kg->kg_estcpu++;
+#endif
+ resetpriority(kg);
+ if (kg->kg_pri.pri_level >= PUSER)
+ kg->kg_pri.pri_level = kg->kg_pri.pri_user;
}
Most of the changes here are to fix style bugs. In the NEW_SCHED case,
the relative weights for each priority are determined by the niceweights[]
table. kg->kg_estcpu is limited only by INT_MAX and priorities are
assigned according to relative values of kg->kg_estcpu (code for this is
not shown). The NEW_SCHED case has not been tried since before SMPng
broke scheduling some more by compressing the priority ranges.
Bruce
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