>Synopsis: server freezes under heavy CPU usage
>Category: kernel
>Environment:
System : OpenBSD 7.7
Details : OpenBSD 7.7-current (GENERIC.MP) #21: Tue Jun
17 17:40:27 MDT 2025
dera...@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP
Architecture: OpenBSD.amd64
Machine : amd64
>Description:
This machine is a Dell PowerEdge R440 with 16 CPUs and 128GM of RAM.
It freezes under heavy CPU usage, specially with lots of threads.
This started with 7.7-release + syspatches but continues with a
-current as of today.
No panic, nothing, just freezes. Can't even force into ddb (with
ddb.console=1). During last test, top(1) froze with this last output:
load averages: 10.73, 11.12, 10.53 test 16:46:44
125 processes: 93 idle, 32 on processor up 0 days 00:59:55
16 CPUs: 17.7% user, 51.5% nice, 3.6% sys, 1.1% spin, 1.1% intr, 25.0% idle
Memory: Real: 13G/37G act/tot Free: 87G Cache: 22G Swap: 0K/64G
PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
60756 root 64 0 13G 13G onproc/1 - 35:05 100.78% python3.12
27129 root 10 20 9124K 1532K onproc/2 fsleep 8:31 75.98% semaphore
42272 root 10 20 9644K 1540K onproc/4 fsleep 8:36 75.83% semaphore
60257 root 10 20 9644K 1560K onproc/14 fsleep 8:32 74.76% semaphore
27054 root 64 0 384K 328K onproc/7 - 0:26 71.24% rm
58070 root 10 0 15M 4428K sleep/13 fsleep 23:45 36.04% nfdump
11522 root 10 20 9636K 1524K onproc/0 fsleep 8:44 31.93% semaphore
40359 root 10 20 9648K 1556K onproc/2 fsleep 8:44 29.88% semaphore
72237 root 10 20 9632K 1520K onproc/0 fsleep 8:41 27.20% semaphore
42031 root 10 20 9648K 1576K onproc/8 fsleep 8:39 27.10% semaphore
97960 root 10 20 9644K 1536K onproc/8 fsleep 8:39 26.46% semaphore
76525 root 10 0 95M 57M sleep/12 fsleep 10:01 12.84% nfdump
68093 root 10 20 96M 64M sleep/3 fsleep 10:07 12.11% nfdump
94072 root -5 20 27M 11M sleep/3 biowait 4:42 1.03% pigz
52734 root 2 0 1640K 2740K sleep/4 kqread 0:37 0.98% top
84043 root 10 20 27M 11M sleep/3 inode 2:07 0.34% pigz
95028 root 10 20 27M 11M sleep/4 inode 2:09 0.15% pigz
66823 root 10 20 26M 11M sleep/0 inode 2:07 0.05% pigz
59751 root 2 0 2768K 3244K sleep/0 kqread 0:09 0.05% tmux
58124 root -22 0 0K 4K sleep/1 - 37:01 0.00% idle1
59513 root -22 0 0K 4K sleep/2 - 36:27 0.00% idle2
Any recommendations on what could help debugging?
>How-To-Repeat:
Start lots of thread-intensive programs, like pigz(1), nfdump(1), etc.
I also had a simple C test program using SYSV IPC semaphores running.
The problem seems to require a reasonable number of CPUs (16 or more)
to manifest itself.
>Fix:
Unknown.
Thanks,
--Kor
