[PATCH v9 13/13] docs: add io_queue flag to isolcpus

Aaron Tomlin
2026-03-31T06:26:09Z

From: Daniel Wagner <wagi@kernel.org>

The io_queue flag informs multiqueue device drivers where to place
hardware queues. Document this new flag in the isolcpus
command-line argument description.

Reviewed-by: Aaron Tomlin <atomlin@atomlin.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Daniel Wagner <wagi@kernel.org>
---
.../admin-guide/kernel-parameters.txt | 22 ++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 03a550630644..9ed7c3ecd158 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2816,7 +2816,6 @@ Kernel parameters
"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
@@ -2839,6 +2838,27 @@ Kernel parameters
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.
+
+ The io_queue configuration takes precedence
+ over managed_irq. When io_queue is used,
+ managed_irq placement constrains have no
+ effect.
+
+ Note: Offlining housekeeping CPUS which serve
+ isolated CPUs will be rejected. Isolated CPUs
+ need to be offlined before offlining the
+ housekeeping CPUs.
+
+ 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]
--
2.51.0