workqueue: implement "workqueue.debug_force_rr_cpu" debug feature
Workqueue used to guarantee local execution for work items queued
without explicit target CPU. The guarantee is gone now which can
break some usages in subtle ways. To flush out those cases, this
patch implements a debug feature which forces round-robin CPU
selection for all such work items.
The debug feature defaults to off and can be enabled with a kernel
parameter. The default can be flipped with a debug config option.
If you hit this commit during bisection, please refer to 041bd12e272c
("Revert "workqueue: make sure delayed work run in local cpu"") for
more information and ping me.
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 87d40a7..cda2ead 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -4230,6 +4230,17 @@
The default value of this parameter is determined by
the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
+ workqueue.debug_force_rr_cpu
+ Workqueue used to implicitly guarantee that work
+ items queued without explicit CPU specified are put
+ on the local CPU. This guarantee is no longer true
+ and while local CPU is still preferred work items
+ may be put on foreign CPUs. This debug option
+ forces round-robin CPU selection to flush out
+ usages which depend on the now broken guarantee.
+ When enabled, memory and cache locality will be
+ impacted.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.