focal (7) tuned-profiles-cpu-partitioning.7.gz

NAME

       tuned-profiles-cpu-partitioning - Partition CPUs into isolated and housekeeping.

DESCRIPTION

       The cpu-partitioning profile partitions the system CPUs into isolated and housekeeping CPUs. This profile
       is intended to be used for latency-sensitive workloads.

       An isolated CPU incurs reduced jitter and reduced  interruptions  by  the  kernel.  This  is  achived  by
       clearing the CPU from user-space processes, movable kernel threads, interruption handlers, kernel timers,
       etc. The only fixed source of interruptions is the 1Hz tick maintained by the kernel to  keep  CPU  usage
       statistics.  Otherwise, the incurred jitter and interruptions, if any, depend on the kernel services used
       by the thread running on the isolated CPU. Threads that run a busy loop without doing system calls,  such
       as  user-space  drivers  that  access  the  hardware directly, are only expected to be interrupted once a
       second by the 1Hz tick.

       A housekeeping CPU is the opposite  of  an  isolated  CPU.  Housekeeping  CPUs  run  all  daemons,  shell
       processes,  kernel threads, interruption handlers and work that can be dispatched from isolated CPUs such
       as disk I/O, RCU work, timers, etc.

CONFIGURATION

       The cpu-partitioning profile is  configured  by  editing  the  /etc/tuned/cpu-partitioning-variables.conf
       file. There are two configuration options:

       isolated_cores=<CPU-LIST>
              List  of  CPUs  to  isolate.  This option is mandatory. Any CPUs not in this list is automatically
              considered a housekeeping CPU.

       no_balance_cores=<CPU-LIST>
              List of CPUs not be considered by the  kernel  when  doing  system  wide  process  load-balancing.
              Usually, this list should be the same as isolated_cores=. This option is optional.

IMPORTANT NOTES

       * The  system  should  be  rebooted  after  applying  the  cpu-partitioning profile for the first time or
         changing its configuration

       * The cpu-partitioning profile can be used in bare-metal and virtual machines

       * The cpu-partitioning profile does not use the kernel's isolcpus= feature

       * On a NUMA system, it is recommended to have at least one housekeeping CPU per NUMA node

       * The cpu-partitioning profile does not support isolating the L3 cache. This means  that  a  housekeeping
         CPU  can  still  thrash  cache  entries  pertaining  to  isolated  CPUs. It is recommended to use cache
         isolation technologies to remedy this problem, such as Intel's Cache Allocation Technology

       * Whether or not the kernel is going to be able to deactivate the tick on isolated CPUs depend on  a  few
         factors  concerning  the  running  thread behavior.  Please, consult the nohz_full documentation in the
         kernel to learn more

       * The Linux real-time project has put together a document on the best practices  for  writting  real-time
         applications. Even though the cpu-partitioning profile does not guarantee real-time response time, much
         of the techniques for writting real-time applications also apply for applications intended to run under
         the cpu-partitioning profile. Please, refer to this document at https://rt.wiki.kernel.org

FILES

       /etc/tuned/cpu-partitioning-variables.conf
       /etc/tuned/tuned-main.conf

SEE ALSO

       tuned(8)    tuned-adm(8)    tuned-profiles(7)    tuned-profiles-realtime(7)    tuned-profiles-nfv-host(7)
       tuned-profiles-nfv-guest(7)

AUTHOR

       Jaroslav Škarvada <jskarvad@redhat.com>
       Luiz Capitulino <lcapitulino@redhat.com>
       Andrew Theurer <atheurer@redhat.com>