From: Paul E. McKenney Date: Mon, 27 Sep 2021 17:54:22 +0000 (-0700) Subject: doc: Remove obsolete kernel-per-CPU-kthreads RCU_FAST_NO_HZ advice X-Git-Tag: v5.17-rc1~160^2~3 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=db4cb76861282604cf14fb362f507bb587d676ba;p=thirdparty%2Fkernel%2Flinux.git doc: Remove obsolete kernel-per-CPU-kthreads RCU_FAST_NO_HZ advice This document advises building with both CONFIG_NO_HZ=y and CONFIG_RCU_FAST_NO_HZ=y. However, CONFIG_NO_HZ=y offloads callbacks from all nohz_full CPUs, and CPUs with offloaded callbacks do not benefit from CONFIG_RCU_FAST_NO_HZ=y. Quite the opposite: CONFIG_RCU_FAST_NO_HZ=y simply adds a bit of idle entry/exit overhead. This commit therefore changes that advice to only CONFIG_NO_HZ=y. Signed-off-by: Paul E. McKenney --- diff --git a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst index 5e51ee5b03589..e4a5fc26f1a9d 100644 --- a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst +++ b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst @@ -208,7 +208,7 @@ Do at least one of the following: 2. Enable RCU to do its processing remotely via dyntick-idle by doing all of the following: - a. Build with CONFIG_NO_HZ=y and CONFIG_RCU_FAST_NO_HZ=y. + a. Build with CONFIG_NO_HZ=y. b. Ensure that the CPU goes idle frequently, allowing other CPUs to detect that it has passed through an RCU quiescent state. If the kernel is built with CONFIG_NO_HZ_FULL=y,