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Openwrt 15.05 enable taskset


1 Install taskset in openwrt

Taskset can be enabled in busybox.

Base system  --->
  <*> busybox
    Miscellaneous Utilities  --->
      [*] taskset

After select, build the busybox package.

make package/busybox/{clean,prepare,compile} V=s

After build, download the built busybox to board.

In board, do the following operations:

tftp -gr busybox 192.168.1.10
chmod +x busybox
ln -s busybox taskset

2 Test taskset command

2.1 View the CPU Affinity of a running Process

To retrieve the CPU affinity information of a process, use the
following format. taskset returns the current CPU affinity in a
hexadecimal bitmask format.

taskset -p <PID>

For example, to check the CPU affinit of /sbin/procd with PID 1:

root@AP-:/tmp# ./taskset -p 1                                                   
pid 1's current affinity mask: f

In this example, the returned affinity (represented in a hexadecimal
bitmask) corresponds to “1111” in binary format, which means the
process can run on any of 4 different CPU cores (from 0 to 3).

The lowest bit a hexadecimal bitmask corresponds to core ID 0, the
second lowest bit from the right to core ID 1, the third lowest bit
to core ID 2, etc.

2.2 Pin a Running Process to Particular CPU Core(s)

taskset -p <COREMASK> <PID>

e.g.

root@AP-:/tmp# ./taskset -p 0x1 1                                               
pid 1's current affinity mask: f                                                
pid 1's new affinity mask: 1

2.3 Launch a Program on Specific CPU Cores

taskset also allows you to launch a new program as pinned to
specific CPU cores. For that, use the following format.

taskset <COREMASK> <EXECUTABLE>

For example, to launch vlc on a CPU core 0, use the following command.

taskset 0x1 vlc

3 Knowledge

One operating system (OS) support often exploited to run performance-critical
applications on multi-core processors is so-called “processor affinity”
or “CPU pinning”. This is an OS-specific feature that “binds” a running
process or program to particular CPU core(s).

Binding a program to specific CPU cores can be benefical in several
scenarios. For example, when an application with highly cache-bound
workload runs together with other CPU-intensive jobs, pinning the
application to a specific CPU would reduce CPU cache misses. Also,
when two processes communicate via shared memory intensively, scheduling
both processes on the cores in the same NUMA domain would speed up
their performance.

To assign particular CPU cores to a program or process, you can use
taskset, a command line tool for retrieving or setting a process’
CPU affinity on Linux.