[PATCH v3 03/20] kconfig: Provide PREFERRED_CPU option

[Shrikanth Hegde]

Introduce a new config named PREFERRED_CPU.

This helps to:
- Avoid the code bloat when PREFERRED_CPU=n. In that cases preferred
  is same as online.
- Avoid the ifdeffery around PREFERRED_CPU in many files.

Since par-avirtual use case is the main driving force of this
feature, make it default for kernels with PARAVIRT=y

Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
---
 kernel/Kconfig.preempt | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 88c594c6d7fc..495252fef768 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -192,3 +192,16 @@ config SCHED_CLASS_EXT
 	  For more information:
 	    Documentation/scheduler/sched-ext.rst
 	    https://github.com/sched-ext/scx
+
+config PREFERRED_CPU
+	bool "Dynamic vCPU management based on steal time"
+	default y if PARAVIRT && SMP
+	help
+	This feature helps to reduce the steal time in paravirtualised
+	environment, there by reducing vCPU preemption. Reducing vCPU
+	preemption provides improved lock holder preemption and reduces
+	cost of vCPU preemption in the host.
+
+	By default preferred CPUs will be same as online CPUs. Depending
+	on the steal time when steal monitor is enabled, preferred CPUs
+	could become subset of online CPUs.
-- 
2.47.3