Ps command does not display the nice value for processes with the SCHED_BATCH
scheduler policy, only for SCHED_OTHER.
Boinc (http://boinc.berkeley.edu/) client runs project processing jobs on
Linux using SCHED_BATCH scheduler policy and nice value 19. The nice value
is not displayable by ps.
Steps to Reproduce:
1. Run process using SCHED_BATCH scheduler policy with nice value.
./test-schedbatch 18 &
2. Display process details:
ps -o pid,ppid,user,comm,cls,nice
Results before:
[mike@rockover c]$ ps -o pid,ppid,user,comm,cls,nice
PID PPID USER COMMAND CLS NI
18205 2540 mike bash TS 0
20552 18205 mike test-schedbatch B -
20553 18205 mike ps TS 0
[mike@rockover c]$ awk '{printf "%5d %-17s %1d %2d\n", $1, $2, $41, $19}'
/proc/20552/stat
20552 (test-schedbatch) 3 18
Results after this patch:
[mike@rockover c]$ ps -o pid,ppid,user,comm,cls,nice
PID PPID USER COMMAND CLS NI
18205 2540 mike bash TS 0
20552 18205 mike test-schedbatch B 18
20553 18205 mike ps TS 0
Additional info: Here is the fragment from the sched_setscheduler(2) manual
page on the subject:
SCHED_BATCH: Scheduling batch processes
(Since Linux 2.6.16.) SCHED_BATCH can only be used at static
priority 0. This policy is similar to SCHED_OTHER in that it
schedules the process according to its dynamic priority (based on the
nice value). The difference is that this policy will cause the
scheduler to always assume that the process is CPU-intensive.
Consequently, the scheduler will apply a small scheduling penalty with
respect to wakeup behaviour, so that this process is mildly disfavored
in scheduling decisions.
This policy is useful for workloads that are noninteractive, but do
not want to lower their nice value, and for workloads that want a
determin- istic scheduling policy without interactivity causing extra
preemptions (between the workload's tasks).
Reference: https://bugzilla.redhat.com/show_bug.cgi?id=741090
Acked-by: Jaromir Capik <jcapik@redhat.com>
Acked-by: Sami Kerola <kerolasa@iki.fi>
Signed-off-by: Mike Fleetwood <mike.fleetwood@googlemail.com>
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