Author: jeff
Date: Sat Mar 8 00:35:06 2014
New Revision: 262917
URL: http://svnweb.freebsd.org/changeset/base/262917
Log:
- Make runq_steal_from more aggressive. Previously it would examine only
a single priority queue. If that queue had a thread or threads which
could not be migrated we would fail to steal load. This could cause
starvation in situations where cores are idle.
Submitted by: Doug Kilpatrick <dkilpatr...@isilon.com>
Tested by: pho
Reviewed by: mav
Sponsored by: EMC / Isilon Storage Division
Modified:
head/sys/kern/sched_ule.c
Modified: head/sys/kern/sched_ule.c
==============================================================================
--- head/sys/kern/sched_ule.c Sat Mar 8 00:14:40 2014 (r262916)
+++ head/sys/kern/sched_ule.c Sat Mar 8 00:35:06 2014 (r262917)
@@ -1057,32 +1057,27 @@ runq_steal_from(struct runq *rq, int cpu
struct rqhead *rqh;
struct thread *td, *first;
int bit;
- int pri;
int i;
rqb = &rq->rq_status;
bit = start & (RQB_BPW -1);
- pri = 0;
first = NULL;
again:
for (i = RQB_WORD(start); i < RQB_LEN; bit = 0, i++) {
if (rqb->rqb_bits[i] == 0)
continue;
- if (bit != 0) {
- for (pri = bit; pri < RQB_BPW; pri++)
- if (rqb->rqb_bits[i] & (1ul << pri))
- break;
- if (pri >= RQB_BPW)
+ if (bit == 0)
+ bit = RQB_FFS(rqb->rqb_bits[i]);
+ for (; bit < RQB_BPW; bit++) {
+ if ((rqb->rqb_bits[i] & (1ul << bit)) == 0)
continue;
- } else
- pri = RQB_FFS(rqb->rqb_bits[i]);
- pri += (i << RQB_L2BPW);
- rqh = &rq->rq_queues[pri];
- TAILQ_FOREACH(td, rqh, td_runq) {
- if (first && THREAD_CAN_MIGRATE(td) &&
- THREAD_CAN_SCHED(td, cpu))
- return (td);
- first = td;
+ rqh = &rq->rq_queues[bit + (i << RQB_L2BPW)];
+ TAILQ_FOREACH(td, rqh, td_runq) {
+ if (first && THREAD_CAN_MIGRATE(td) &&
+ THREAD_CAN_SCHED(td, cpu))
+ return (td);
+ first = td;
+ }
}
}
if (start != 0) {
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