[PATCH v8 12/12] docs: add io_queue flag to isolcpus

[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>
---
 Documentation/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 747a55abf4946bb9efe320f0f62fdcd1560b0a71..4161d4277a7086f2a3726617826c50888eefb260 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2653,7 +2653,6 @@
 			  "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
@@ -2676,6 +2675,27 @@
 			  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