[PATCH v12 13/13] docs: add io_queue flag to isolcpus

Aaron Tomlin
2026-04-23T03:08:50Z

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@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
[atomlin: Refined io_queue kernel parameter documentation]
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
.../admin-guide/kernel-parameters.txt | 30 ++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cf3807641d89..e2d798351964 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2810,7 +2810,6 @@ 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
@@ -2833,6 +2832,35 @@ Kernel parameters
housekeeping CPUs has no influence on those
queues.

+ io_queue
+ Applicable to managed IRQs only. Restrict
+ multiqueue hardware queue allocation to online
+ housekeeping CPUs. This guarantees that all
+ managed hardware completion interrupts are routed
+ exclusively to housekeeping cores, shielding
+ isolated CPUs from I/O interruptions even if they
+ initiated the request.
+
+ The io_queue configuration takes precedence over
+ managed_irq. When io_queue is used, managed_irq
+ placement constraints have no effect.
+
+ Note: Using io_queue restricts the number of
+ allocated hardware queues to match the number of
+ housekeeping CPUs. This prevents MSI-X vector
+ exhaustion and forces isolated CPUs to share
+ submission queues.
+
+ Note: Offlining housekeeping CPUs which serve
+ isolated CPUs will fail. The isolated CPUs must
+ be offlined before offlining the housekeeping
+ CPUs.
+
+ Note: When I/O is submitted by an application on
+ an isolated CPU, the hardware completion
+ interrupt is handled entirely by a housekeeping
+ CPU.
+
The format of <cpu-list> is described above.

iucv= [HW,NET]
--
2.51.0