Display scheduler class for a process in linux
Posted by Martin Bach on June 15, 2010
The ps command in the ways I use it most (ps -ef and ps auxwww) doesn’t display the scheduling class for a process. Oracle have cunningly released a patchset to update Grid Infrastructure that changes the scheduling class from the VKTM and LMSn ASM processes to “Timeshare” instead of Realtime.
So far so good, but I had no idea how to display the scheduling class of a process so some man page reading and Internet research were in order. After some digging around I found out that using the BSD command line syntax combined with the “–format” option does the trick. The difficult bit was in figuring out which format identifiers to use. All the information ps can get about a process are recorded in /proc/pid/stat. Parsing this with a keen eye however proves difficult due to the sheer number of fields in the file. So back to using ps (1).
Here’s the example. Before applying the workaround to the patch, Oracle ASM’s VKTM (virtual keeper of time) and LMSn (global cache services process) run with TS priority:
[oracle@rac11gr2node2 ~]$ ps ax --format uname,pid,ppid,tty,cmd,cls,pri,rtprio \ >| egrep "(vktm|lms)" | grep asm grid 4296 1 ? asm_vktm_+ASM2 TS 24 - grid 4318 1 ? asm_lms0_+ASM2 TS 24 -
After applying the workaround the scheduling class changed:
[oracle@rac11gr2node1 ~]$ ps ax --format uname,pid,ppid,tty,cmd,cls,pri,rtprio | egrep "(vktm|lms)" | grep asm grid 2352 1 ? asm_vktm_+ASM1 RR 41 1 grid 2374 1 ? asm_lms0_+ASM1 RR 41 1
Notice how the cls field changed, and also that the rtprio is now populated. I have learned something new today.