Chapter 3. Reviewing a system by using the tuna interface

The tuna tool reduces the complexity of performing tuning tasks. Use tuna to adjust scheduler tunables, tune thread priority, IRQ handlers, and to isolate CPU cores and sockets. By using the tuna tool, you can perform the following operations:

  • List the CPUs on a system.
  • List the interrupt requests (IRQs) currently running on a system.
  • Change policy and priority information about threads.
  • Display the current policies and priorities of a system.

3.1. Installing the tuna tool

The tuna tool is designed to be used on a running system. This allows application-specific measurement tools to see and analyze system performance immediately after changes have been made.

Procedure

  • Install the tuna tool: 

    # dnf install tuna

Verification steps

  • Display the available tuna CLI options: 

    # tuna -h

Additional resources

  • tuna(8) man page

3.2. Viewing the system status by using the tuna tool

You can use the tuna command-line interface (CLI) tool to view the system status.

Prerequisites

Procedure

  1. View the current policies and priorities: 

    # tuna show_threads
pid   SCHED_ rtpri affinity             cmd
1      OTHER     0      0,1            init
2       FIFO    99        0     migration/0
3      OTHER     0        0     ksoftirqd/0
4       FIFO    99        0      watchdog/0

    Alternatively, to view a specific thread corresponding to a PID or matching a command name, enter: 

    # tuna show_threads -t pid_or_cmd_list

    The pid_or_cmd_list argument is a list of comma-separated PIDs or command-name patterns.

  2. Depending on you scenario, perform one of the following actions:

  3. Save the changed configuration: 

    # tuna save filename

    This command saves only currently running kernel threads. Processes that are not running are not saved.

Additional resources

  • tuna(8) man page on your system

3.3. Tuning CPUs by using the tuna tool

The tuna tool commands can target individual CPUs. By using the tuna tool, you can perform the following actions:

Isolate CPUs
All tasks running on the specified CPU move to the next available CPU. Isolating a CPU makes this CPU unavailable by removing it from the affinity mask of all threads.
Include CPUs
Allows tasks to run on the specified CPU.
Restore CPUs
Restores the specified CPU to its previous configuration.

Prerequisites

Procedure

  1. List all CPUs and specify the list of CPUs to be affected by the command: 

    # ps ax | awk 'BEGIN { ORS="," }{ print $1 }'
PID,1,2,3,4,5,6,8,10,11,12,13,14,15,16,17,19

  2. Display the thread list in the tuna interface: 

    # tuna show_threads -t 'thread_list from above cmd'

  3. Specify the list of CPUs to be affected by a command: 

    # *tuna [command] --cpus cpu_list *

    The cpu_list argument is a list of comma-separated CPU numbers, for example, --cpus 0,2.

    To add a specific CPU to the current cpu_list, use, for example, --cpus +0.

  4. Depending on your scenario, perform one of the following actions:

    • To isolate a CPU, enter: 

      # tuna isolate --cpus cpu_list

    • To include a CPU, enter: 

      # tuna include --cpus cpu_list

  5. To use a system with four or more processors, make all ssh threads run on CPU 0 and 1 and all http threads on CPU 2 and 3: 

    # tuna move --cpus 0,1 -t ssh*
# tuna move --cpus 2,3 -t http\*

Verification steps

  • Display the current configuration and verify that the changes were applied: 

    # tuna show_threads -t ssh*

pid   SCHED_  rtpri  affinity   voluntary   nonvoluntary   cmd
855   OTHER   0      0,1        23           15            sshd

# tuna show_threads -t http\*
pid   SCHED_  rtpri  affinity   voluntary   nonvoluntary   cmd
855   OTHER   0       2,3        23           15           http

Additional resources

  • /proc/cpuinfo file
  • tuna(8) man page on your system

3.4. Tuning IRQs by using the tuna tool

The /proc/interrupts file records the number of interrupts per IRQ, the type of interrupt, and the name of the device that is located at that IRQ.

Prerequisites

Procedure

  1. View the current IRQs and their affinity: 

    # tuna show_irqs
# users            affinity
0 timer                   0
1 i8042                   0
7 parport0                0

  2. Specify the list of IRQs to be affected by a command: 

    # tuna [command] --irqs irq_list --cpus cpu_list

    The irq_list argument is a list of comma-separated IRQ numbers or user-name patterns.

    Replace [command] with, for example, --spread.

  3. Move an interrupt to a specified CPU: 

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

# tuna move --irqs 128 --cpus 3

    Replace 128 with the irq_list argument and 3 with the cpu_list argument.

    The cpu_list argument is a list of comma-separated CPU numbers, for example, --cpus 0,2. For more information, see Tuning CPUs by using the tuna tool.

Verification steps

  • Compare the state of the selected IRQs before and after moving any interrupt to a specified CPU: 

    # tuna show_irqs --irqs 128
     users            affinity
 128 iwlwifi                 3

Additional resources

  • /procs/interrupts file
  • tuna(8) man page on your system