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| -rw-r--r-- | Documentation/timers/no_hz.rst | 10 |
1 files changed, 3 insertions, 7 deletions
diff --git a/Documentation/timers/no_hz.rst b/Documentation/timers/no_hz.rst index 20ad23a6c618..f8786be15183 100644 --- a/Documentation/timers/no_hz.rst +++ b/Documentation/timers/no_hz.rst @@ -184,16 +184,12 @@ There are situations in which idle CPUs cannot be permitted to enter either dyntick-idle mode or adaptive-tick mode, the most common being when that CPU has RCU callbacks pending. -The CONFIG_RCU_FAST_NO_HZ=y Kconfig option may be used to cause such CPUs -to enter dyntick-idle mode or adaptive-tick mode anyway. In this case, -a timer will awaken these CPUs every four jiffies in order to ensure -that the RCU callbacks are processed in a timely fashion. - -Another approach is to offload RCU callback processing to "rcuo" kthreads +Avoid this by offloading RCU callback processing to "rcuo" kthreads using the CONFIG_RCU_NOCB_CPU=y Kconfig option. The specific CPUs to offload may be selected using The "rcu_nocbs=" kernel boot parameter, which takes a comma-separated list of CPUs and CPU ranges, for example, -"1,3-5" selects CPUs 1, 3, 4, and 5. +"1,3-5" selects CPUs 1, 3, 4, and 5. Note that CPUs specified by +the "nohz_full" kernel boot parameter are also offloaded. The offloaded CPUs will never queue RCU callbacks, and therefore RCU never prevents offloaded CPUs from entering either dyntick-idle mode |