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 <frederic@kernel.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20241030175253.125248-3-longman@redhat.com

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3872bc6ec49d63772755504966ae70113f24a1db..3fa0b4e65275af7eaa475a464c6d0e406380b7d8 100644 (file)
--- 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 5345e11f3d44f74362095c55839cf63de9ff4083..6a686322ce3cbbc0d641ea52b7cf1128d79fa084 100644 (file)
--- 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;
                }