[PATCH] Documentation/kernel-parameters: Remove "Deprecated" from isolcpus=

[PATCH] Documentation/kernel-parameters: Remove "Deprecated" from isolcpus=

[Sebastian Andrzej Siewior]

The isolcpus= option has been marked as deprecated in 2017. Back then it
was desired for the domain sub option to be configured dynamically at
runtime instead using this boot command line which provides a static
configuration. In the meantime this option was extended by other sub
options which don't have runtime counterpart or it does not make sense
to provide one.

The deprecated part always referred to the default `domain' sub option
but it was not obvious. Also the reasoning behind the deprecation is
sort of dubious: There is nothing wrong with a static configuration if
there is no desired to reconfigure. This is useful on systems which
have one purpose and the CPU partition configuration is not changed for
the entire lifetime.

Remove the "Deprecated" note. Remove the part of the description which
suggest to use cpuset.sched_load_balance and instead point to the
documentation file which explains how to use cpusets to configure this
at runtime.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 Documentation/admin-guide/kernel-parameters.txt | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 4d0f545fb3ec5..367931fe8da56 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2755,7 +2755,6 @@ Kernel parameters
 			Format: <RDP>,<reset>,<pci_scan>,<verbosity>
 
 	isolcpus=	[KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
-			[Deprecated - use cpusets instead]
 			Format: [flag-list,]<cpu-list>
 
 			Specify one or more CPUs to isolate from disturbances
@@ -2780,11 +2779,10 @@ Kernel parameters
 			  Isolate from the general SMP balancing and scheduling
 			  algorithms. Note that performing domain isolation this way
 			  is irreversible: it's not possible to bring back a CPU to
-			  the domains once isolated through isolcpus. It's strongly
-			  advised to use cpusets instead to disable scheduler load
-			  balancing through the "cpuset.sched_load_balance" file.
-			  It offers a much more flexible interface where CPUs can
-			  move in and out of an isolated set anytime.
+			  the domains once isolated through this boot time
+			  configuration. Use cpusets for a dynamic configuration
+			  which can be altered at runtime. For details see
+			  Documentation/admin-guide/cpu-isolation.rst.
 
 			  You can move a process onto or off an "isolated" CPU via
 			  the CPU affinity syscalls or cpuset.
-- 
2.53.0

Re: [PATCH] Documentation/kernel-parameters: Remove "Deprecated" from isolcpus=

[Steven Rostedt]

On Mon, 27 Apr 2026 17:07:39 +0200
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> The isolcpus= option has been marked as deprecated in 2017. Back then it
> was desired for the domain sub option to be configured dynamically at
> runtime instead using this boot command line which provides a static
> configuration. In the meantime this option was extended by other sub
> options which don't have runtime counterpart or it does not make sense
> to provide one.
> 
> The deprecated part always referred to the default `domain' sub option
> but it was not obvious. Also the reasoning behind the deprecation is
> sort of dubious: There is nothing wrong with a static configuration if
> there is no desired to reconfigure. This is useful on systems which
> have one purpose and the CPU partition configuration is not changed for
> the entire lifetime.
> 
> Remove the "Deprecated" note. Remove the part of the description which
> suggest to use cpuset.sched_load_balance and instead point to the
> documentation file which explains how to use cpusets to configure this
> at runtime.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)

Acked-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve

Re: [PATCH] Documentation/kernel-parameters: Remove "Deprecated" from isolcpus=

[Waiman Long]

On 4/27/26 11:07 AM, Sebastian Andrzej Siewior wrote:
> The isolcpus= option has been marked as deprecated in 2017. Back then it
> was desired for the domain sub option to be configured dynamically at
> runtime instead using this boot command line which provides a static
> configuration. In the meantime this option was extended by other sub
> options which don't have runtime counterpart or it does not make sense
> to provide one.
>
> The deprecated part always referred to the default `domain' sub option
> but it was not obvious. Also the reasoning behind the deprecation is
> sort of dubious: There is nothing wrong with a static configuration if
> there is no desired to reconfigure. This is useful on systems which
> have one purpose and the CPU partition configuration is not changed for
> the entire lifetime.
>
> Remove the "Deprecated" note. Remove the part of the description which
> suggest to use cpuset.sched_load_balance and instead point to the
> documentation file which explains how to use cpusets to configure this
> at runtime.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>   Documentation/admin-guide/kernel-parameters.txt | 10 ++++------
>   1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 4d0f545fb3ec5..367931fe8da56 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2755,7 +2755,6 @@ Kernel parameters
>   			Format: <RDP>,<reset>,<pci_scan>,<verbosity>
>   
>   	isolcpus=	[KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
> -			[Deprecated - use cpusets instead]
>   			Format: [flag-list,]<cpu-list>
>   
>   			Specify one or more CPUs to isolate from disturbances
> @@ -2780,11 +2779,10 @@ Kernel parameters
>   			  Isolate from the general SMP balancing and scheduling
>   			  algorithms. Note that performing domain isolation this way
>   			  is irreversible: it's not possible to bring back a CPU to
> -			  the domains once isolated through isolcpus. It's strongly
> -			  advised to use cpusets instead to disable scheduler load
> -			  balancing through the "cpuset.sched_load_balance" file.
> -			  It offers a much more flexible interface where CPUs can
> -			  move in and out of an isolated set anytime.
> +			  the domains once isolated through this boot time
> +			  configuration. Use cpusets for a dynamic configuration
> +			  which can be altered at runtime. For details see
> +			  Documentation/admin-guide/cpu-isolation.rst.
>   
>   			  You can move a process onto or off an "isolated" CPU via
>   			  the CPU affinity syscalls or cpuset.
Acked-by: Waiman Long <longman@redhat.com>

Re: [PATCH] Documentation/kernel-parameters: Remove "Deprecated" from isolcpus=

[Jonathan Corbet]

Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:

> The isolcpus= option has been marked as deprecated in 2017. Back then it
> was desired for the domain sub option to be configured dynamically at
> runtime instead using this boot command line which provides a static
> configuration. In the meantime this option was extended by other sub
> options which don't have runtime counterpart or it does not make sense
> to provide one.
>
> The deprecated part always referred to the default `domain' sub option
> but it was not obvious. Also the reasoning behind the deprecation is
> sort of dubious: There is nothing wrong with a static configuration if
> there is no desired to reconfigure. This is useful on systems which
> have one purpose and the CPU partition configuration is not changed for
> the entire lifetime.
>
> Remove the "Deprecated" note. Remove the part of the description which
> suggest to use cpuset.sched_load_balance and instead point to the
> documentation file which explains how to use cpusets to configure this
> at runtime.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)

Applied, thanks.

jon

Re: [PATCH] Documentation/kernel-parameters: Remove "Deprecated" from isolcpus=

[Frederic Weisbecker]

Le Mon, Apr 27, 2026 at 05:07:39PM +0200, Sebastian Andrzej Siewior a écrit :
> The isolcpus= option has been marked as deprecated in 2017. Back then it
> was desired for the domain sub option to be configured dynamically at
> runtime instead using this boot command line which provides a static
> configuration. In the meantime this option was extended by other sub
> options which don't have runtime counterpart or it does not make sense
> to provide one.
> 
> The deprecated part always referred to the default `domain' sub option
> but it was not obvious. Also the reasoning behind the deprecation is
> sort of dubious: There is nothing wrong with a static configuration if
> there is no desired to reconfigure. This is useful on systems which
> have one purpose and the CPU partition configuration is not changed for
> the entire lifetime.
> 
> Remove the "Deprecated" note. Remove the part of the description which
> suggest to use cpuset.sched_load_balance and instead point to the
> documentation file which explains how to use cpusets to configure this
> at runtime.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Acked-by: Frederic Weisbecker <frederic@kernel.org>

-- 
Frederic Weisbecker
SUSE Labs