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Message-ID: <20241030175253.125248-3-longman@redhat.com>
Date: Wed, 30 Oct 2024 13:52:51 -0400
From: Waiman Long <longman@...hat.com>
To: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Valentin Schneider <vschneid@...hat.com>,
Frederic Weisbecker <frederic@...nel.org>
Cc: linux-kernel@...r.kernel.org,
Phil Auld <pauld@...hat.com>,
Waiman Long <longman@...hat.com>
Subject: [RESEND PATCH v4 2/4] 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@...nel.org>
Signed-off-by: Waiman Long <longman@...hat.com>
Acked-by: Frederic Weisbecker <frederic@...nel.org>
---
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 8337d0fed311..4e664587943f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2424,7 +2424,9 @@
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;
}
--
2.43.5
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