From 1174b9344bc7e7989439cad207fcd94eaab028db Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Wed, 30 Oct 2024 13:52:51 -0400 Subject: [PATCH] sched/isolation: Make "isolcpus=nohz" equivalent to "nohz_full" The "isolcpus=nohz" boot parameter and flag were used to disable tick when running a single task. Nowsdays, this "nohz" flag is seldomly used as it is included as part of the "nohz_full" parameter. Extend this flag to cover other kernel noises disabled by the "nohz_full" parameter to make them equivalent. This also eliminates the need to use both the "isolcpus" and the "nohz_full" parameters to fully isolated a given set of CPUs. Suggested-by: Frederic Weisbecker Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Acked-by: Frederic Weisbecker Link: https://lore.kernel.org/r/20241030175253.125248-3-longman@redhat.com --- Documentation/admin-guide/kernel-parameters.txt | 4 +++- kernel/sched/isolation.c | 6 +++++- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 3872bc6ec49d..3fa0b4e65275 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2432,7 +2432,9 @@ specified in the flag list (default: domain): nohz - Disable the tick when a single task runs. + Disable the tick when a single task runs as well as + disabling other kernel noises like having RCU callbacks + offloaded. This is equivalent to the nohz_full parameter. A residual 1Hz tick is offloaded to workqueues, which you need to affine to housekeeping through the global diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 5345e11f3d44..6a686322ce3c 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -209,9 +209,13 @@ static int __init housekeeping_isolcpus_setup(char *str) int len; while (isalpha(*str)) { + /* + * isolcpus=nohz is equivalent to nohz_full. + */ if (!strncmp(str, "nohz,", 5)) { str += 5; - flags |= HK_FLAG_TICK; + flags |= HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | + HK_FLAG_RCU | HK_FLAG_MISC | HK_FLAG_KTHREAD; continue; } -- 2.50.1