Chapter 19. Improving latency using the tuna CLI
You can use the tuna
CLI to improve latency on your system. The tuna CLI, for RHEL 9, includes the command line interface, which is based on the argparse
parsing module. The interface provides the following capabilities:
- A more standardized menu of commands and options
-
With the interface, you can use predefined inputs and
tuna
ensures that the inputs are of the right type - Generates usage help messages automatically, on how to use parameters and provides error messages with invalid arguments
19.1. Prerequisites
-
The
tuna
and thepython-linux-procfs
packages are installed. - You have root permissions on the system.
19.2. The tuna
CLI
The tuna
command-line interface (CLI) is a tool to help you make tuning changes to your system.
The tuna
tool is designed to be used on a running system, and changes take place immediately. This allows any application-specific measurement tools to see and analyze system performance immediately after changes have been made.
The tuna
CLI now has a set of commands, which formerly were the action options. These commands are:
- isolate
-
Move all threads and IRQs away from the
CPU-LIST
. - include
-
Configure all threads to run on a
CPU-LIST
. - move
-
Move specific entities to the
CPU-LIST
. - spread
-
Spread the selected entities over the
CPU-LIST
. - priority
-
Set the thread scheduler tunables, such as
POLICY
andRTPRIO
. - run
- Fork a new process and run the command.
- save
-
Save
kthreads
sched
tunables
toFILENAME
. - apply
- Apply changes defined in the profile.
- show_threads
- Display a thread list.
- show_irqs
-
Display the
IRQ
list. - show_configs
- Display the existing profile list.
- what_is
- Provide help about selected entities.
- gui
- Start the graphical user interface (GUI).
You can view the commands with the tuna -h
command. For each command, there are optional arguments, which you can view with the tuna <command> -h
command. For example, with the tuna isolate -h
command, you can view the options for isolate
.
19.3. Isolating CPUs using the tuna
CLI
You can use the tuna
CLI to isolate interrupts (IRQs) from user processes on different dedicated CPUs to minimize latency in real-time environments. For more information about isolating CPUs, see Interrupt and process binding.
Prerequisites
-
The
tuna
and thepython-linux-procfs
packages are installed. - You have root permissions on the system.
Procedure
Isolate one or more CPUs.
# tuna isolate --cpus=<cpu_list>
cpu_list
is a comma-separated list or a range of CPUs to isolate.For example:
# tuna isolate --cpus=0,1
or
# tuna isolate --cpus=0-5
19.4. Moving interrupts to specified CPUs using the tuna
CLI
You can use the tuna
CLI to move interrupts (IRQs) to dedicated CPUs to minimize or eliminate latency in real-time environments. For more information about moving IRQs, see Interrupt and process binding.
Prerequisites
-
The
tuna
andpython-linux-procfs
packages are installed. - You have root permissions on the system.
Procedure
List the CPUs to which a list of IRQs is attached.
# tuna show_irqs --irqs=<irq_list>
irq_list
is a comma-separated list of the IRQs for which you want to list attached CPUs.For example:
# tuna show_irqs --irqs=128
Attach a list of IRQs to a list of CPUs.
# tuna move --irqs=irq_list --cpus=<cpu_list>
irq_list
is a comma-separated list of the IRQs you want to attach andcpu_list
is a comma-separated list of the CPUs to which they will be attached or a range of CPUs.For example:
# tuna move --irqs=128 --cpus=3
Verification
Compare the state of the selected IRQs before and after moving any IRQ to a specified CPU.
# tuna show_irqs --irqs=128
19.5. Changing process scheduling policies and priorities using the tuna
CLI
You can use the tuna
CLI to change process scheduling policy and priority.
Prerequisites
-
The
tuna
andpython-linux-procfs
packages are installed. You have root permissions on the system.
NoteAssigning the
OTHER
andBATCH
scheduling policies does not require root permissions.
Procedure
View the information for a thread.
# tuna show_threads --threads=<thread_list>
thread_list
is a comma-separated list of the processes you want to display.For example:
# tuna show_threads --threads=42369,42416,43859
Modify the process scheduling policy and the priority of the thread.
# tuna priority scheduling_policy:priority_number --threads=<thread_list>
-
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, where0
is no priority and99
is the highest priority.NoteThe
OTHER
andBATCH
scheduling policies do not require specifying a priority. In addition, the only valid priority (if specified) is0
. TheFIFO
andRR
scheduling policies require a priority of1
or more.For example:
-
# tuna priority FIFO:1 --threads=42369,42416,43859
Verification
- View the information for the thread to ensure that the information changes.
# tuna show_threads --threads=42369,42416,43859