Idle time increases if number of running bash processes exceeds number of cores.
Issue
- high CPU utilization during process
Using the following bash script:
# cat bashtest.sh
until [ 1 = 2 ]; do let x=65535*65535*65535*65535*65535*65535*65535; done
On a system with N cores running N instances of the above script the idle time drops to zero. Running one more copy causes the idle time to increase.
An idle system with 2 cores.
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 0 595472 16444 173728 0 0 58 7 507 870 73 8 19 1 0
0 0 0 595472 16444 173728 0 0 0 28 1027 35 0 0 100 0 0
0 0 0 595472 16444 173728 0 0 0 0 1005 30 0 0 100 0 0
0 0 0 595472 16444 173728 0 0 0 0 1022 29 0 0 100 0 0
0 0 0 595472 16444 173728 0 0 0 0 1003 24 0 0 100 0 0
...
Two copies of the script started:
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r b swpd free buff cache si so bi bo in cs us sy id wa st
...
0 1 0 595472 16448 173724 0 0 0 20 1022 32 0 0 100 1 0
0 0 0 595472 16452 173728 0 0 0 4 1007 34 0 0 98 3 0
1 0 0 595340 16452 173728 0 0 0 0 1029 44 14 2 84 0 0
1 0 0 595340 16452 173728 0 0 0 0 1012 38 45 5 50 0 0
1 0 0 595340 16452 173728 0 0 0 0 1029 50 45 5 50 0 0
2 0 0 595332 16452 173728 0 0 0 0 1013 1774 67 8 25 0 0
2 0 0 595332 16452 173728 0 0 0 0 1020 2725 87 11 2 0 0
2 0 0 595332 16460 173720 0 0 0 56 1004 3267 87 10 2 0 0
...
Idle time is reduced as the system is kept busy. Two more copies started:
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r b swpd free buff cache si so bi bo in cs us sy id wa st
...
3 0 0 595332 16476 173720 0 0 0 12 1002 3061 85 10 4 0 0
2 0 0 595332 16476 173720 0 0 0 0 1018 2888 85 11 4 0 0
3 0 0 594952 16476 173728 0 0 0 0 1015 1216 62 7 31 0 0
4 0 0 594952 16476 173728 0 0 0 0 1019 1667 67 8 26 0 0
3 0 0 594696 16476 173728 0 0 0 0 1011 1648 66 7 27 0 0
2 0 0 594696 16476 173728 0 0 0 0 1020 1336 59 7 34 0 0
4 0 0 594696 16484 173720 0 0 0 56 1006 1858 71 7 22 0 0
...
Idle time increases sharply.
Environment
- Redhat Enterprise Linux 5
Subscriber exclusive content
A Red Hat subscription provides unlimited access to our knowledgebase of over 48,000 articles and solutions.
Close
Welcome! Check out the Getting Started with Red Hat page for quick tours and guides for common tasks.