Date: Sat, 8 Mar 2014 00:35:07 +0000 (UTC) From: Jeff Roberson <jeff@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r262917 - head/sys/kern Message-ID: <201403080035.s280Z7xF036149@svn.freebsd.org>
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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 <dkilpatrick@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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