What are the rcuos/rcuob processes I'm seeing in top?
Solution 1
The key article explaining this is here: https://lwn.net/Articles/522262/
For faster synchronization, many structures in the kernel are "RCU", or read-copy-update. Many threads can read simultaneously without blocking, and threads that want to alter the structure can do so quickly by copying the relevant data to a new location and changing the reference ("removal"). However, the old data must live for some time longer so that reading threads can finish their work. When the old data no longer has readers working on it, it can finally be deleted ("reclamation").
The rcuos, rcuob threads are there to handle the reclamation part of this process. It used to be handled as part of software IRQ, which meant it could take processor power away from critical user processes at inopportune times. By moving this to a bunch of dedicated rcu** threads, the system can be tuned to make this reclamation process less intrusive.
Reducing OS jitter is not the purpose of these threads, though it may be the main reason they exist.
Solution 2
According to the ubuntuforums they are coming from the "Reduce OS Jitter" which is turned on by the following kernel flags
CONFIG_RCU_NOCB_CPU
CONFIG_RCU_NOCB_CPU_ALL
CONFIG_RCU_STALL_COMMON
CONFIG_RCU_USER_QS
Since 13.10 (Saucy) they are enabled by default.
See:
- http://ubuntuforums.org/showthread.php?t=2225218
- https://www.kernel.org/doc/Documentation/kernel-per-CPU-kthreads.txt
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sonicboom
Updated on September 18, 2022Comments
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sonicboom almost 2 years
I ran top, and I see lots of rcuos/rcuob processes. Here's a sample of top output:
top - 21:41:15 up 22 days, 19:20, 1 user, load average: 0.00, 0.01, 0.05 Tasks: 332 total, 1 running, 331 sleeping, 0 stopped, 0 zombie Cpu(s): 0.0%us, 0.0%sy, 0.0%ni, 99.9%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 32910904k total, 2232224k used, 30678680k free, 246636k buffers Swap: 33517564k total, 0k used, 33517564k free, 1048244k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 3098 root 20 0 11.8g 113m 9.9m S 1 0.4 67:57.98 asterisk 12 root 20 0 0 0 0 S 0 0.0 0:53.61 rcuos/3 1130 root 39 19 0 0 0 S 0 0.0 78:26.78 kipmi0 1735 root 20 0 15988 740 540 S 0 0.0 17:34.69 irqbalance 1875 zabbix 20 0 89416 2472 1828 S 0 0.0 12:55.47 zabbix_agentd 1 root 20 0 24316 2288 1336 S 0 0.0 0:05.06 init 2 root 20 0 0 0 0 S 0 0.0 0:00.25 kthreadd 3 root 20 0 0 0 0 S 0 0.0 0:02.40 ksoftirqd/0 5 root 0 -20 0 0 0 S 0 0.0 0:00.00 kworker/0:0H 6 root 20 0 0 0 0 S 0 0.0 0:00.00 kworker/u48:0 8 root 20 0 0 0 0 S 0 0.0 4:55.92 rcu_sched 9 root 20 0 0 0 0 S 0 0.0 1:31.03 rcuos/0 10 root 20 0 0 0 0 S 0 0.0 0:54.04 rcuos/1 11 root 20 0 0 0 0 S 0 0.0 0:53.16 rcuos/2 13 root 20 0 0 0 0 S 0 0.0 0:45.96 rcuos/4 14 root 20 0 0 0 0 S 0 0.0 0:41.84 rcuos/5 15 root 20 0 0 0 0 S 0 0.0 0:02.56 rcuos/6 16 root 20 0 0 0 0 S 0 0.0 0:07.25 rcuos/7 17 root 20 0 0 0 0 S 0 0.0 0:12.06 rcuos/8 18 root 20 0 0 0 0 S 0 0.0 0:12.14 rcuos/9 19 root 20 0 0 0 0 S 0 0.0 0:11.21 rcuos/10 20 root 20 0 0 0 0 S 0 0.0 0:05.66 rcuos/11 21 root 20 0 0 0 0 S 0 0.0 1:39.42 rcuos/12 22 root 20 0 0 0 0 S 0 0.0 0:35.66 rcuos/13 23 root 20 0 0 0 0 S 0 0.0 0:26.46 rcuos/14 24 root 20 0 0 0 0 S 0 0.0 0:00.88 rcuos/15 25 root 20 0 0 0 0 S 0 0.0 0:00.30 rcuos/16 26 root 20 0 0 0 0 S 0 0.0 0:31.93 rcuos/17 27 root 20 0 0 0 0 S 0 0.0 0:18.58 rcuos/18 28 root 20 0 0 0 0 S 0 0.0 0:20.53 rcuos/19 29 root 20 0 0 0 0 S 0 0.0 0:44.95 rcuos/20 30 root 20 0 0 0 0 S 0 0.0 0:01.92 rcuos/21 31 root 20 0 0 0 0 S 0 0.0 0:00.24 rcuos/22 32 root 20 0 0 0 0 S 0 0.0 0:05.01 rcuos/23 33 root 20 0 0 0 0 S 0 0.0 0:00.00 rcu_bh 34 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/0 35 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/1 36 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/2 37 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/3 38 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/4 39 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/5 40 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/6 41 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/7 42 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/8 43 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/9 44 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/10 45 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/11 46 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/12 47 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/13 48 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/14 49 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/15 50 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/16 51 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/17 52 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/18 53 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/19 54 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/20 55 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/21 56 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/22 57 root 20 0 0 0 0 S 0 0.0 0:00.00 rcuob/23 58 root RT 0 0 0 0 S 0 0.0 0:00.87 migration/0 59 root RT 0 0 0 0 S 0 0.0 0:08.47 watchdog/0 60 root RT 0 0 0 0 S 0 0.0 0:08.41 watchdog/1What are these processes?
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Lety almost 10 yearsI guess these process are kernel process related to RCU. Here is useful link on: Understanding RCU when Configuring the Linux Kernel and question same as your is here. -
dschinn1001 over 9 years@sonicboom - good posting - what about it could be too a sort of watching-tool too, about whether a coder is able to code something ? (written by ibm ?) ... - is this a new case for Snowden ?
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