[PATCH v7 10/10] docs: add io_queue flag to isolcpus

[Aaron Tomlin]

On Wed, Jul 02, 2025 at 06:34:00PM +0200, Daniel Wagner wrote:
> The io_queue flag informs multiqueue device drivers where to place
> hardware queues. Document this new flag in the isolcpus
> command-line argument description.
> 
> Signed-off-by: Daniel Wagner <wagi at kernel.org>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f1f2c0874da9ddfc95058c464fdf5dabaf0de713..7594ac5448575cc895ebf7af0fe051d42dc5e0e9 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2590,7 +2590,6 @@
>  			  "number of CPUs in system - 1".
>  
>  			managed_irq
> -
>  			  Isolate from being targeted by managed interrupts
>  			  which have an interrupt mask containing isolated
>  			  CPUs. The affinity of managed interrupts is
> @@ -2613,6 +2612,24 @@
>  			  housekeeping CPUs has no influence on those
>  			  queues.
>  
> +			io_queue
> +			  Isolate from I/O queue work caused by multiqueue
> +			  device drivers. Restrict the placement of
> +			  queues to housekeeping CPUs only, ensuring that
> +			  all I/O work is processed by a housekeeping CPU.
> +
> +			  Housekeeping CPUs that serve isolated CPUs
> +			  cannot be offlined.
> +
> +			  The io_queue configuration takes precedence over
> +			  managed_irq; thus, when io_queue is used,
> +			  managed_irq has no effect.
> +
> +			  Note: When an isolated CPU issues an I/O request,
> +			  it is forwarded to a housekeeping CPU. This will
> +			  trigger a software interrupt on the completion
> +			  path.
> +
>  			The format of <cpu-list> is described above.
>  
>  	iucv=		[HW,NET]
> 
> -- 
> 2.50.0
> 

Reviewed-by: Aaron Tomlin <atomlin at atomlin.com>

-- 
Aaron Tomlin