Chapter 16. Improving latency using the tuna CLI

Procedure

1. List the CPUs to which a list of IRQs is attached.

   # tuna --irqs=<irq_list> --show_irqs

   irq_list is a comma-separated list of the IRQs for which you want to list attached CPUs.

   For example:

   # tuna --irqs=128 --show_irqs
      # users         affinity
    128 iwlwifi          0,1,2,3

2. Attach a list of IRQs to a list of CPUs.

   # tuna --irqs=irq_list --cpus=<cpu_list> --move

   irq_list is a comma-separated list of the IRQs you want to attach and cpu_list is a comma-separated list of the CPUs to which they will be attached or a range of CPUs.

   For example:

   # tuna --irqs=128 --cpus=3 --move

Procedure

1. View the information for a thread.

   # tuna --threads=<thread_list> --show_threads

   thread_list is a comma-separated list of the processes you want to display.

   For example:

   # tuna --threads=rngd --show_threads
                         thread       ctxt_switches
       pid SCHED_ rtpri affinity voluntary nonvoluntary             cmd
     3571   OTHER     0  0,1,2,3    167697          134            rngd

2. Modify the process scheduling policy and the priority of the thread.

   # tuna --threads=<thread_list> --priority scheduling_policy:priority_number

   • thread_list is a comma-separated list of the processes whose scheduling policy and priority you want to display.

   • scheduling_policy is one of the following:

     • OTHER
     • BATCH
     • FIFO - First In First Out
     • RR - Round Robin

   • priority_number is a priority number from 0 to 99, where 0 is no priority and 99 is the highest priority.

     Note

     The OTHER and BATCH scheduling policies do not require specifying a priority. In addition, the only valid priority (if specified) is 0. The FIFO and RR scheduling policies require a priority of 1 or more.

     For example:

     # tuna --threads=rngd --priority FIFO:1