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Chapter 4. Reviewing a system using tuna interface
Use the tuna
tool to adjust scheduler tunables, tune thread priority, IRQ handlers, and isolate CPU cores and sockets. Tuna reduces the complexity of performing tuning tasks.
The tuna
tool performs the following operations:
- Lists the CPUs on a system
- Lists the interrupt requests (IRQs) currently running on a system
- Changes policy and priority information about threads
- Displays the current policies and priorities of a system
4.1. 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:# yum install tuna
Verification
Display the available
tuna
CLI options:# tuna -h
Additional resources
-
tuna(8)
man page on your system
4.2. Viewing the system status using tuna tool
This procedure describes how to view the system status using the tuna
command-line interface (CLI) tool.
Prerequisites
- The tuna tool is installed. For more information, see Installing tuna tool.
Procedure
To view the current policies and priorities:
# tuna --show_threads thread 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
To view a specific thread corresponding to a PID or matching a command name:
# tuna --threads=pid_or_cmd_list --show_threads
The pid_or_cmd_list argument is a list of comma-separated PIDs or command-name patterns.
-
To tune CPUs using the
tuna
CLI, see Tuning CPUs using tuna tool. -
To tune the IRQs using the
tuna
tool, see Tuning IRQs using tuna tool. To 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
4.3. Tuning CPUs using tuna tool
The tuna
tool commands can target individual CPUs.
Using the tuna tool, you can:
Isolate CPUs
- All tasks running on the specified CPU move to the next available CPU. Isolating a CPU makes it 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.
This procedure describes how to tune CPUs using the tuna
CLI.
Prerequisites
- The tuna tool is installed. For more information, see Installing tuna tool.
Procedure
To specify the list of CPUs to be affected by a command:
# tuna --cpus=cpu_list [command]
The cpu_list argument is a list of comma-separated CPU numbers. For example,
--cpus=0,2
. CPU lists can also be specified in a range, for example--cpus=”1-3”
, which would select CPUs 1, 2, and 3.To add a specific CPU to the current cpu_list, for example, use
--cpus=+0
.Replace [command] with, for example,
--isolate
.To isolate a CPU:
# tuna --cpus=cpu_list --isolate
To include a CPU:
# tuna --cpus=cpu_list --include
To use a system with four or more processors, display how to make all the ssh threads run on CPU 0 and 1, and all the
http
threads on CPU 2 and 3:# tuna --cpus=0,1 --threads=ssh\* \ --move --cpus=2,3 --threads=http\* --move
This command performs the following operations sequentially:
- Selects CPUs 0 and 1.
-
Selects all threads that begin with
ssh
. -
Moves the selected threads to the selected CPUs. Tuna sets the affinity mask of threads starting with
ssh
to the appropriate CPUs. The CPUs can be expressed numerically as 0 and 1, in hex mask as 0x3, or in binary as 11. - Resets the CPU list to 2 and 3.
-
Selects all threads that begin with
http
. -
Moves the selected threads to the specified CPUs. Tuna sets the affinity mask of threads starting with
http
to the specified CPUs. The CPUs can be expressed numerically as 2 and 3, in hex mask as 0xC, or in binary as 1100.
Verification
Display the current configuration and verify that the changes were performed as expected:
# tuna --threads=gnome-sc\* --show_threads \ --cpus=0 --move --show_threads --cpus=1 \ --move --show_threads --cpus=+0 --move --show_threads thread ctxt_switches pid SCHED_ rtpri affinity voluntary nonvoluntary cmd 3861 OTHER 0 0,1 33997 58 gnome-screensav thread ctxt_switches pid SCHED_ rtpri affinity voluntary nonvoluntary cmd 3861 OTHER 0 0 33997 58 gnome-screensav thread ctxt_switches pid SCHED_ rtpri affinity voluntary nonvoluntary cmd 3861 OTHER 0 1 33997 58 gnome-screensav thread ctxt_switches pid SCHED_ rtpri affinity voluntary nonvoluntary cmd 3861 OTHER 0 0,1 33997 58 gnome-screensav
This command performs the following operations sequentially:
-
Selects all threads that begin with the
gnome-sc
threads. - Displays the selected threads to enable the user to verify their affinity mask and RT priority.
- Selects CPU 0.
-
Moves the
gnome-sc
threads to the specified CPU, CPU 0. - Shows the result of the move.
- Resets the CPU list to CPU 1.
-
Moves the
gnome-sc
threads to the specified CPU, CPU 1. - Displays the result of the move.
- Adds CPU 0 to the CPU list.
-
Moves the
gnome-sc
threads to the specified CPUs, CPUs 0 and 1. - Displays the result of the move.
-
Selects all threads that begin with the
Additional resources
-
/proc/cpuinfo
file -
tuna(8)
man page on your system
4.4. Tuning IRQs using 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.
This procedure describes how to tune the IRQs using the tuna
tool.
Prerequisites
- The tuna tool is installed. For more information, see Installing tuna tool.
Procedure
To view the current IRQs and their affinity:
# tuna --show_irqs # users affinity 0 timer 0 1 i8042 0 7 parport0 0
To specify the list of IRQs to be affected by a command:
# tuna --irqs=irq_list [command]
The irq_list argument is a list of comma-separated IRQ numbers or user-name patterns.
Replace [command] with, for example,
--spread
.To move an interrupt to a specified CPU:
# tuna --irqs=128 --show_irqs # users affinity 128 iwlwifi 0,1,2,3 # tuna --irqs=128 --cpus=3 --move
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 using tuna tool.
Verification
Compare the state of the selected IRQs before and after moving any interrupt to a specified CPU:
# tuna --irqs=128 --show_irqs # users affinity 128 iwlwifi 3
Additional resources
-
/procs/interrupts
file -
tuna(8)
man page on your system