NetBSD Problem Report #43561
From www@NetBSD.org Sat Jul 3 08:30:29 2010
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Date: Sat, 3 Jul 2010 08:30:29 +0000 (UTC)
From: witold.wnuk@gmail.com
Reply-To: witold.wnuk@gmail.com
To: gnats-bugs@NetBSD.org
Subject: Thread waiting, CPU idling
X-Send-Pr-Version: www-1.0
>Number: 43561
>Category: kern
>Synopsis: Thread waiting, CPU idling
>Confidential: no
>Severity: non-critical
>Priority: high
>Responsible: kern-bug-people
>State: closed
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Sat Jul 03 08:35:00 +0000 2010
>Closed-Date: Tue Apr 10 08:21:43 +0000 2018
>Last-Modified: Tue Apr 10 08:21:43 +0000 2018
>Originator: Witold Jan Wnuk
>Release: NetBSD-current
>Organization:
>Environment:
NetBSD foster 5.99.33 NetBSD 5.99.33 (FOSTER) #23: Sat Jul 3 09:07:28 CEST 2010 w@foster:/home/w/NetBSD/src/sys/arch/i386/compile/FOSTER i386
>Description:
On multiprocessor system sched_balance (sys/kern/kern_runq.c) fails to select CPU with one thread in run queue.
>How-To-Repeat:
Compile and run one copy for each CPU. Inspect CPU idle time.
int
main()
{
while (1)
;
}
Problem described by Sad Clouds in http://mail-index.netbsd.org/tech-userlevel/2010/04/16/msg003515.html is likely also a manifestation of this.
>Fix:
Workaround - add one bit of precision to r_avgcount calculation:
Index: sys/kern/kern_runq.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_runq.c,v
retrieving revision 1.30
diff -u -r1.30 kern_runq.c
--- sys/kern/kern_runq.c 3 Mar 2010 00:47:30 -0000 1.30
+++ sys/kern/kern_runq.c 3 Jul 2010 07:43:20 -0000
@@ -78,7 +78,7 @@
uint32_t r_bitmap[PRI_COUNT >> BITMAP_SHIFT];
/* Counters */
u_int r_count; /* Count of the threads */
- u_int r_avgcount; /* Average count of threads */
+ u_int r_avgcount1; /* Average count of threads x 2 */
u_int r_mcount; /* Count of migratable threads */
/* Runqueues */
queue_t r_rt_queue[PRI_RT_COUNT];
@@ -523,12 +523,12 @@
ci_rq = ci->ci_schedstate.spc_sched_info;
/* Average count of the threads */
- ci_rq->r_avgcount = (ci_rq->r_avgcount + ci_rq->r_mcount) >> 1;
+ ci_rq->r_avgcount1 = (ci_rq->r_avgcount1 + (ci_rq->r_mcount << 1)) >> 1;
/* Look for CPU with the highest average */
- if (ci_rq->r_avgcount > highest) {
+ if (ci_rq->r_avgcount1 > highest) {
hci = ci;
- highest = ci_rq->r_avgcount;
+ highest = ci_rq->r_avgcount1;
}
}
@@ -625,7 +625,7 @@
}
/* Reset the counter, and call the balancer */
- ci_rq->r_avgcount = 0;
+ ci_rq->r_avgcount1 = 0;
sched_balance(ci);
tci = worker_ci;
tspc = &tci->ci_schedstate;
@@ -734,7 +734,7 @@
return NULL;
/* Reset the counter, and call the balancer */
- ci_rq->r_avgcount = 0;
+ ci_rq->r_avgcount1 = 0;
sched_balance(ci);
cci = worker_ci;
cspc = &cci->ci_schedstate;
@@ -871,14 +871,14 @@
ci_rq = spc->spc_sched_info;
(*pr)("Run-queue (CPU = %u):\n", ci->ci_index);
- (*pr)(" pid.lid = %d.%d, r_count = %u, r_avgcount = %u, "
+ (*pr)(" pid.lid = %d.%d, r_count = %u, r_avgcount1 = %u, "
"maxpri = %d, mlwp = %p\n",
#ifdef MULTIPROCESSOR
ci->ci_curlwp->l_proc->p_pid, ci->ci_curlwp->l_lid,
#else
curlwp->l_proc->p_pid, curlwp->l_lid,
#endif
- ci_rq->r_count, ci_rq->r_avgcount, spc->spc_maxpriority,
+ ci_rq->r_count, ci_rq->r_avgcount1, spc->spc_maxpriority,
spc->spc_migrating);
i = (PRI_COUNT >> BITMAP_SHIFT) - 1;
do {
>Release-Note:
>Audit-Trail:
From: Hubert Feyrer <hubert@feyrer.de>
To: witold.wnuk@gmail.com, gnats-bugs@NetBSD.org
Cc: Hubert Feyrer <hubertf@netbsd.org>
Subject: Re: kern/43561: Thread waiting, CPU idling
Date: Thu, 22 Dec 2016 20:55:41 +0100 (CET)
FWIW,
code was committed to -current today that might fix this issue.
See PR kern/51615 and the following URL and its threat for more
information:
http://mail-index.netbsd.org/source-changes/2016/12/22/msg080093.html
If this resolves your issue, please let me know and I can close the PR.
- Hubert
State-Changed-From-To: open->feedback
State-Changed-By: dholland@NetBSD.org
State-Changed-When: Tue, 06 Jun 2017 03:19:56 +0000
State-Changed-Why:
If you're still there please check the commit cited...
State-Changed-From-To: feedback->closed
State-Changed-By: dholland@NetBSD.org
State-Changed-When: Tue, 10 Apr 2018 08:21:43 +0000
State-Changed-Why:
Feedback timeout.
>Unformatted:
(Contact us)
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