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I want to see if my process makes a lot of context switches. I also want to see how manpulating task groups affects the number of context switches.

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What OS? What version? What kernel? –  Mikel May 25 '12 at 16:48
GNU/Linux 2.6.18 –  luntain May 25 '12 at 17:28
Check /proc/[pid]/status –  Kevin May 25 '12 at 17:34

4 Answers 4

pidstat(1) - Report statistics for Linux tasks. According to man pidstat it's so easy as just pidstat -w …

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I executed "watch -n0.5 pidstat -w -I -p 5876" command but the output is 0 (for both cswch/s nvcswch/s). Does this command work for linux version - 2.6.39-400.214.4.el6uek.x86_64 ? –  Andy Dufresne Mar 19 at 6:52
This command should work just fine. But beware you're using it wrong because when you don't specify report interval „tasks statistics are to be reported for the time since system startup (boot).” similar to vmstat, iostat and others. So if current statistics is needed instead of watch'ing simply run it with one second interval. –  poige Mar 19 at 12:46
If I don't do watch, how do I see the numbers updating continuously? Executing the command "pidstat -w -I -p 5876 5" the command just waits for 5 seconds and then prints the output (again as 0). It does not run continuously as I was expecting (I know that this is contradicting to what pidstat's man page says - linux.die.net/man/1/pidstat). My OS is Oracle Linux Server 6.4. –  Andy Dufresne Mar 21 at 10:57
Does ` pidstat -w -l -p SELF 1` work for you? –  poige Mar 21 at 16:11

You can view information about your process's context switches in /proc/<pid>/status.

$ pid=307
$ grep ctxt /proc/$pid/status
voluntary_ctxt_switches:        41
nonvoluntary_ctxt_switches:     16

To see these numbers updating continuously, run

$ # Update twice a second.
$ watch -n.5 grep ctxt /proc/$pid/status

To get just the numbers, run

$ grep ctxt /proc/$pid/status | awk '{ print $2 }'
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I tried the above watch command but the output is just 1 (for voluntary and involuntary context switch). My linux kernal version is 2.6.39-400.214.4.el6uek.x86_64. Is the output dependant on the linux version? –  Andy Dufresne Mar 19 at 6:49
Paste your output here please. –  Evan Teitelman Mar 20 at 19:05
Its the same as mentioned in the answere - "watch -n.5 grep ctxt /proc/5647/status" –  Andy Dufresne Mar 21 at 10:52

To get a record of an entire process run, you can use the GNU time utility (don't confuse it with the bash builtin) with the -v option. Here's an example with unrelated lines of output removed:

$ `which time` -v ls
a.out  exception_finder.cpp  log.txt
    Command being timed: "ls"
    Voluntary context switches: 1
    Involuntary context switches: 2
    Exit status: 0
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Write the following script to file (ctx.sh). with ctx.sh <core> you will see all the processes running on a given core and changing nv-context switches will be highlighted. Looking at this, you will be able to identify which are the competing processes for the core.


if [[ $# -eq 0 ]]
   echo "Usage:"
   echo "$0 <core>"
   exit 1

if [[ -z $2 ]]
   watch -d -n .2 $0 $1 nw

ps -Leo lastcpu:1,tid,comm | grep "^$1 " | awk '{printf $3": ";system("cut -d\" \" -f3  /proc/"$2"/task/"$2"/schedstat 2>/dev/null")}' | sort -k 1 | column -t
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