Red Hat Bugzilla – Bug 88013
Scheduler doesn't background nice 19 jobs
Last modified: 2015-01-04 17:02:26 EST
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Description of problem:
Using the rawhide kernel above (and with the errata RedHat 7.3 kernel
2.4.18-27.7.x), CPU-bound nice +19 jobs are given too much cpu with respect to
CPU-bound nice 0 jobs.
For instance on a 433MHz PII (also tried 1400MHz Athlon & P4 2700MHz)
5:29pm up 35 min, 3 users, load average: 2.14, 1.80, 0.99
69 processes: 65 sleeping, 4 running, 0 zombie, 0 stopped
CPU states: 90.6% user, 0.1% system, 9.1% nice, 0.0% idle
Mem: 384772K av, 76876K used, 307896K free, 0K shrd, 7428K buff
Swap: 1028152K av, 0K used, 1028152K free 25948K cached
PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
1497 jss 25 0 1000 1000 380 R 90.4 0.2 9:49 cpufloattest
1635 jss 39 19 956 956 340 R N 9.1 0.2 0:51 cpufloattest
So 1/10 of the power goes to the nice 19 job, even though they are both cpu
bound. There's no way of giving the nice 19 job lower priority (AFAIK).
On a Compaq Tru64 4.1B system:
load averages: 2.30, 2.23, 2.19 17:31:14
48 processes: 3 running, 14 sleeping, 31 idle
CPU states: 99.5% user, 0.0% nice, 0.4% system, 0.0% idle
Memory: Real: 77M/235M act/tot Virtual: 9M/1223M use/tot Free: 118M
PID USERNAME PRI NICE SIZE RES STATE TIME CPU COMMAND
211277 jss 59 0 2120K 188K run 6:23 99.70% a.out
203876 jmb65 63 19 12M 9322K run 316:20 0.00% tree
The nice 0 job gets 99.7% of the CPU - a far better deal.
Can the scheduler be fixed to lower the priority of batch nice +19 jobs?
Otherwise a patch to implement something like the SCHED_BATCH patch would be useful.
(Also nice 10 jobs get 1/3 of the cpu - I'd suggest that's too much).
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Run nice 0 foreground job
2. Run nice 19 background job
3. 19 job gets 6-10% of the CPU
I tend to agree - processes which are niced at 19 are those which "if you can
run, fine..." I run several things at 19 (time updates, random signature
generation, etc.) that do not need any sort of priority (not 9% at least). This
would probably include Ingo Molnar (author of the O(1) scheduler for the kernel
- also works for Red Hat).
It does bring up a good point for the central kernel maintainers - gauging
scheduling performance versus commerical UNIX kernels would be interesting to
see how Linux fares out.
This situation is getting worse. Using 2.4.20-13.7 on 7.3 gives 15% to the
niced-19 process on a P4.
It would be great if RH were to include Ingo Molnar's SCHED_BATCH feature to
allow background execution of jobs when there are no other jobs running.
I've contacted Ingo Molnar and he says he'll look into the nice 19 issue.