WIP: minimal CPU to fit IRQ count

Signed-off-by: Francesco Romani <fromani@redhat.com>

Author: ffromani

pkg/performanceprofile/profilecreator/autosize/autosize.go

@@ -30,6 +30,12 @@ import (
 // Objective:
 // We want to maximize x_w, or, equivalently, minimize x_c
 
+const (
+	// x86 limit. 256 hardware entries, of those 32 reserved. 256-32 = 224.
+	// see: https://en.wikipedia.org/wiki/Interrupt_request
+	maxIRQsPerPhysicalCore int = 224
+)
+
 const (
 	defaultPenaltyWeight                 float64 = 100.0
 	defaultReservedRatioInitial          float64 = 0.0625 // 1/16. determined empirically. Use only as initial value.
@@ -65,7 +71,7 @@ type Params struct {
 }
 
 func (p Params) String() string {
-	return fmt.Sprintf("cpus=%d offline=%v SMTLevel=%v devices=%d (userNetworking=%v)", p.totalCPUs, p.OfflinedCPUCount, p.smtLevel, p.DeviceCount, p.UserLevelNetworking)
+	return fmt.Sprintf("cpus=%d offline=%v SMTLevel=%v devices=%d (req=%v userNetworking=%v)", p.totalCPUs, p.OfflinedCPUCount, p.smtLevel, p.DeviceCount, p.MinCPUs(), p.UserLevelNetworking)
 }
 
 func setupMachineData(p *Params) error {
@@ -82,6 +88,13 @@ func setupMachineData(p *Params) error {
 	return nil
 }
 
+func (p Params) MinCPUs() int {
+	if !p.UserLevelNetworking { // TODO explain why
+		return 0
+	}
+	return (p.DeviceCount + (maxIRQsPerPhysicalCore - 1)) / maxIRQsPerPhysicalCore
+}
+
 func (p Params) TotalCPUs() int {
 	return p.totalCPUs
 }
@@ -193,6 +206,9 @@ func objective(p Params, x []float64) float64 {
 	// Don't exceed total CPUs
 	hardPenalty += defaultPenaltyWeight * math.Pow(math.Max(0, x_c+x_w-float64(p.TotalCPUs())), 2)
 
+	// Allocate as minimum what is needed to fit the desired amount of devices, thus IRQs
+	hardPenalty += defaultPenaltyWeight * math.Pow(math.Max(0, float64(p.MinCPUs())-x_c), 2)
+
 	// Meet the control plane/infra requirement to avoid the workload to starve
 	hardPenalty += defaultPenaltyWeight * math.Pow(math.Max(0, p.controlPlaneRequirement(x_w)-x_c), 2)
 

pkg/performanceprofile/profilecreator/cmd/root.go

@@ -171,6 +171,7 @@ func NewRootCommand() *cobra.Command {
 			}
 			if isAutosizeEnabled(pcArgs) {
 				params := autosize.Params{
+					DeviceCount:         pcArgs.DeviceCount,
 					OfflinedCPUCount:    pcArgs.OfflinedCPUCount,
 					UserLevelNetworking: (pcArgs.UserLevelNetworking != nil && *pcArgs.UserLevelNetworking),
 					MachineData:         nodesHandlers[0], // assume all nodes equal, pick the easiest
@@ -433,6 +434,7 @@ type ProfileCreatorArgs struct {
 	PerPodPowerManagement       *bool  `json:"per-pod-power-management,omitempty"`
 	EnableHardwareTuning        bool   `json:"enable-hardware-tuning,omitempty"`
 	Autosize                    *bool  `json:"autosize,omitempty"`
+	DeviceCount                 int    `json:"device-count,omitempty"`
 	// internal only this argument not passed by the user
 	// but detected automatically
 	createForHypershift bool
@@ -454,6 +456,7 @@ func (pca *ProfileCreatorArgs) AddFlags(flags *pflag.FlagSet) {
 	flags.BoolVar(&pca.EnableHardwareTuning, "enable-hardware-tuning", false, "Enable setting maximum cpu frequencies")
 	flags.StringVar(&pca.NodePoolName, "node-pool-name", "", "Node pool name corresponding to the target machines (HyperShift only)")
 	flags.BoolVar(pca.Autosize, "autosize", false, "autosize the control plane")
+	flags.IntVar(&pca.DeviceCount, "device-count", 0, "Number of expected devices (TODO)")
 }
 
 func makePerformanceProfileFrom(profileData ProfileData) (runtime.Object, error) {