Cannot avoid context-switches on a process launched alone on a CPU

Question

I am investigating how run a process on a dedicated CPU in order to avoid context-switches. On my Ubuntu, I isolated two CPUs using the kernel parameters \"isolcpus=3,7\" an

Answer 1

Today, I obtained more clues regarding my problem I realized that I had to investigate deeply what was happening in the Kernel scheduler. I found these two pages:

• Ftrace Linux Kernel Tracing
• ftrace - Function Tracer

I enabled scheduler tracing while my application was running like that:

# sudo bash
# cd /sys/kernel/debug/tracing
# echo 1 > options/function-trace ; echo function_graph > current_tracer ; echo 1 > tracing_on ; echo 0 > tracing_max_latency ; taskset -c 7 [path-to-my-program]/TestCpuset ; echo 0 > tracing_on
# cat trace

As my program was launched on CPU 7 (taskset -c 7), I have to filter the "trace" output

# grep " 7)" trace

I can then search for transitions, from one process to another one:

# grep " 7)" trace | grep "=>"
 ...
 7)  TestCpu-4753  =>  kworker-5866 
 7)  kworker-5866  =>  TestCpu-4753 
 7)  TestCpu-4753  =>   watchdo-26  
 7)   watchdo-26   =>  TestCpu-4753 
 7)  TestCpu-4753  =>  kworker-5866 
 7)  kworker-5866  =>  TestCpu-4753 
 7)  TestCpu-4753  =>  kworker-5866 
 7)  kworker-5866  =>  TestCpu-4753 
 7)  TestCpu-4753  =>  kworker-5866 
 7)  kworker-5866  =>  TestCpu-4753 
 ...

Bingo! It seems that the context switches I am tracking are transitions to:

• kworker
• watchdog

I now have to find:

• what are exactly these processes/threads? (it seems that they are handled by the kernel)
• Can I avoid them to run on my dedicated CPUs?

For course, once again I would appreciate any help :-P