change the interface

RATIONALE.md

@@ -223,6 +223,17 @@ result, not a parameter. The only impact would be to new plugins or those
 ported to WebAssembly. We do not expect limiting the scores to two billion
 above the valid range to be a practical concern for these authors.
 
+### Why does the Permit function return a uint32 representing milliseconds for the timeout, not `time.Duration`?
+
+`framework.PermitPlugin` returns `time.Duration` to represent the timeout.
+`time.Duration` is int64 underneath and 1 time.Duration represents 1 nanosecond.
+
+Given the scheduling throughput in the upstream kube-scheduler is around 300 pods/s, 
+that is, 3+ milliseconds per pod,
+we consider a millisecond-level timeout with uint32 to be sufficiently fine-grained.
+
+Also, tha maximum timeout is around 24 days, which also should be large enough.
+
 ## Why do we return a non-status, second numeric result as an i32?
 
 Most compilers that target WebAssembly Core Specification 1.0, the only REC

guest/api/types.go

@@ -17,8 +17,6 @@
 package api
 
 import (
-	"time"
-
 	"sigs.k8s.io/kube-scheduler-wasm-extension/guest/api/proto"
 )
 
@@ -130,7 +128,8 @@ type ReservePlugin interface {
 type PermitPlugin interface {
 	Plugin
 
-	Permit(state CycleState, p proto.Pod, nodeName string) (*Status, time.Duration)
+	// Note: This is uint32, not time.Duration. See /RATIONALE.md for why.
+	Permit(state CycleState, p proto.Pod, nodeName string) (status *Status, timeoutMilliSeconds uint32)
 }
 
 // PreBindPlugin is a WebAssembly implementation of framework.PreBindPlugin.

guest/internal/mem/mem.go

@@ -53,15 +53,6 @@ func BytesToPtr(b []byte) (uint32, uint32) {
 	return uint32(uintptr(ptr)), uint32(len(b))
 }
 
-// Int64ToPtr returns a pointer for the given int64 number in a way compatible
-// with WebAssembly numeric types.
-// The returned pointer aliases the number hence it must be kept alive until ptr
-// is no longer needed.
-func Int64ToPtr(n int64) uint32 {
-	ptr := unsafe.Pointer(&n)
-	return uint32(uintptr(ptr))
-}
-
 // Update is for decoding values from memory. The updater doesn't keep a
 // reference to the underlying bytes, so we don't need to copy them.
 func Update(

guest/permit/permit.go

@@ -18,12 +18,9 @@
 package permit
 
 import (
-	"runtime"
-
 	"sigs.k8s.io/kube-scheduler-wasm-extension/guest/api"
 	"sigs.k8s.io/kube-scheduler-wasm-extension/guest/internal/cyclestate"
 	"sigs.k8s.io/kube-scheduler-wasm-extension/guest/internal/imports"
-	"sigs.k8s.io/kube-scheduler-wasm-extension/guest/internal/mem"
 	"sigs.k8s.io/kube-scheduler-wasm-extension/guest/internal/plugin"
 )
 
@@ -42,7 +39,7 @@ var permit api.PermitPlugin
 //
 //	type permitPlugin struct{}
 //
-//	func (permitPlugin) Permit(state api.CycleState, p proto.Pod, nodeName string) (status *api.Status, timeout time.Duration)
+//	func (permitPlugin) Permit(state api.CycleState, p proto.Pod, nodeName string) (status *api.Status, timeout uint32)
 //		// Write state you need on Permit
 //	}
 func SetPlugin(permitPlugin api.PermitPlugin) {
@@ -54,12 +51,12 @@ func SetPlugin(permitPlugin api.PermitPlugin) {
 }
 
 // prevent unused lint errors (lint is run with normal go).
-var _ func() uint32 = _permit
+var _ func() uint64 = _permit
 
 // _permit is only exported to the host.
 //
 //export permit
-func _permit() uint32 {
+func _permit() uint64 {
 	if permit == nil { // Then, the user didn't define one.
 		// Unlike most plugins we always export permit so that we can reset
 		// the cycle state: return success to avoid no-op overhead.
@@ -70,9 +67,7 @@ func _permit() uint32 {
 	nodeName := imports.NodeName()
 	status, timeout := permit.Permit(cyclestate.Values, pod, nodeName)
 
-	ptr := mem.Int64ToPtr(int64(timeout))
-	setTimeoutResult(ptr)
-	runtime.KeepAlive(timeout) // untir ptr is no longer needed.
-
-	return imports.StatusToCode(status)
+	// Pack the score and status code into a single WebAssembly 1.0 compatible
+	// result
+	return (uint64(imports.StatusToCode(status)) << uint64(32)) | uint64(timeout)
 }

guest/testdata/cyclestate/main.go

@@ -20,7 +20,6 @@ package main
 
 import (
 	"os"
-	"time"
 	"unsafe"
 
 	"sigs.k8s.io/kube-scheduler-wasm-extension/guest/api"
@@ -190,7 +189,7 @@ func (statePlugin) Unreserve(state api.CycleState, pod proto.Pod, nodeName strin
 	mustFilterState(state)
 }
 
-func (statePlugin) Permit(state api.CycleState, pod proto.Pod, nodeName string) (status *api.Status, timeout time.Duration) {
+func (statePlugin) Permit(state api.CycleState, pod proto.Pod, nodeName string) (status *api.Status, timeout uint32) {
 	mustFilterState(state)
 	return
 }

guest/testdata/permit/main.go

@@ -35,13 +35,13 @@ func main() {
 
 type permitPlugin struct{}
 
-func (permitPlugin) Permit(state api.CycleState, pod proto.Pod, nodeName string) (*api.Status, time.Duration) {
+func (permitPlugin) Permit(state api.CycleState, pod proto.Pod, nodeName string) (*api.Status, uint32) {
 	status, timeout := api.StatusCodeSuccess, time.Duration(0)
 	if nodeName == "bad" {
 		status = api.StatusCodeError
 	} else if nodeName == "wait" {
 		status = api.StatusCodeWait
 		timeout = 10 * time.Second
 	}
-	return &api.Status{Code: status, Reason: "name is " + nodeName}, timeout
+	return &api.Status{Code: status, Reason: "name is " + nodeName}, uint32(timeout.Milliseconds())
 }

scheduler/plugin/guest.go

@@ -251,10 +251,10 @@ func (g *guest) permit(ctx context.Context) (*framework.Status, time.Duration) {
 		return framework.AsStatus(decorateError(g.out, guestExportPermit, err)), 0
 	}
 
-	timeout := paramsFromContext(ctx).resultTimeout
-	statusCode := int32(callStack[0])
+	statusCode := int32(callStack[0] >> 32)
+	timeoutMilliSeconds := int32(callStack[0])
 	statusReason := paramsFromContext(ctx).resultStatusReason
-	return framework.NewStatus(framework.Code(statusCode), statusReason), timeout
+	return framework.NewStatus(framework.Code(statusCode), statusReason), time.Duration(timeoutMilliSeconds) * time.Millisecond
 }
 
 // preBind calls guestExportPreBind.
@@ -355,8 +355,8 @@ func detectInterfaces(exportedFns map[string]wazeroapi.FunctionDefinition) (inte
 			}
 			e |= iReservePlugin
 		case guestExportPermit:
-			if len(f.ParamTypes()) != 0 || !bytes.Equal(f.ResultTypes(), []wazeroapi.ValueType{i32}) {
-				return 0, fmt.Errorf("wasm: guest exports the wrong signature for func[%s]. should be () -> (i32)", name)
+			if len(f.ParamTypes()) != 0 || !bytes.Equal(f.ResultTypes(), []wazeroapi.ValueType{i64}) {
+				return 0, fmt.Errorf("wasm: guest exports the wrong signature for func[%s]. should be () -> (i64)", name)
 			}
 			e |= iPermitPlugin
 		case guestExportPreBind:

scheduler/plugin/host.go

@@ -19,7 +19,6 @@ package wasm
 import (
 	"context"
 	"encoding/json"
-	"time"
 
 	"github.com/tetratelabs/wazero"
 	wazeroapi "github.com/tetratelabs/wazero/api"
@@ -50,7 +49,6 @@ const (
 	k8sSchedulerResultNominatedNodeName   = "result.nominated_node_name"
 	k8sSchedulerResultStatusReason        = "result.status_reason"
 	k8sSchedulerResultNormalizedScoreList = "result.normalized_score_list"
-	k8sSchedulerResultTimeout             = "result.timeout"
 	k8sSchedulerHandleEventRecorderEventf = "handle.eventrecorder.eventf"
 	k8sSchedulerHandleRejectWaitingPod    = "handle.reject_waiting_pod"
 )
@@ -120,9 +118,6 @@ func instantiateHostScheduler(ctx context.Context, runtime wazero.Runtime, guest
 		NewFunctionBuilder().
 		WithGoModuleFunction(wazeroapi.GoModuleFunc(host.k8sHandleRejectWaitingPodFn), []wazeroapi.ValueType{i32, i32, i32, i32}, []wazeroapi.ValueType{}).
 		WithParameterNames("buf", "buf_len").Export(k8sSchedulerHandleRejectWaitingPod).
-		NewFunctionBuilder().
-		WithGoModuleFunction(wazeroapi.GoModuleFunc(k8sSchedulerResultTimeoutFn), []wazeroapi.ValueType{i32}, []wazeroapi.ValueType{}).
-		WithParameterNames("ptr").Export(k8sSchedulerResultTimeout).
 		Instantiate(ctx)
 }
 
@@ -177,9 +172,6 @@ type stack struct {
 
 	// resultNormalizedScoreList is returned by guest.normalizedscoreFn
 	resultNormalizedScoreList framework.NodeScoreList
-
-	// resultTimeout is returned by guest.permitFn
-	resultTimeout time.Duration
 }
 
 func paramsFromContext(ctx context.Context) *stack {
@@ -437,18 +429,6 @@ func k8sSchedulerResultNormalizedScoreListFn(ctx context.Context, mod wazeroapi.
 	paramsFromContext(ctx).resultNormalizedScoreList = MapToNodeScoreList(nodeScoreList)
 }
 
-// k8sSchedulerResultTimeoutFn is a function used by the wasm guest to set the
-// timeout result from guestExportPermit.
-func k8sSchedulerResultTimeoutFn(ctx context.Context, mod wazeroapi.Module, stack []uint64) {
-	ptr := uint32(stack[0])
-
-	n, ok := mod.Memory().ReadUint64Le(ptr)
-	if !ok {
-		panic("out of memory reading timeout")
-	}
-	paramsFromContext(ctx).resultTimeout = time.Duration(int64(n))
-}
-
 // Converts a list of framework.NodeScore to a map with node names as keys and their scores as integer values.
 func NodeScoreListToMap(nodeScoreList []framework.NodeScore) map[string]int {
 	scoreMap := make(map[string]int)

scheduler/plugin/plugin_test.go

@@ -61,7 +61,7 @@ func Test_guestPool_bindingCycles(t *testing.T) {
 
 	_, status := pl.PreFilter(ctx, nil, pod)
 	if !status.IsSuccess() {
-		t.Fatalf("prefilter failed: %v", status)
+		t.Fatalf("prefilter failed: %v", status.Reasons())
 	}
 
 	if pl.GetScheduledPodUID() != pod.UID {
@@ -71,7 +71,7 @@ func Test_guestPool_bindingCycles(t *testing.T) {
 	// pod is going to the binding cycle.
 	status, _ = pl.Permit(ctx, nil, pod, "node")
 	if !status.IsSuccess() {
-		t.Fatalf("filter failed: %v", status)
+		t.Fatalf("permit failed: %v", status.Reasons())
 	}
 
 	if len(pl.GetBindingCycles()) != 1 {
@@ -82,7 +82,7 @@ func Test_guestPool_bindingCycles(t *testing.T) {
 
 	_, status = pl.PreFilter(ctx, nil, nextPod)
 	if !status.IsSuccess() {
-		t.Fatalf("PreFilter failed: %v", status)
+		t.Fatalf("PreFilter failed: %v", status.Reasons())
 	}
 
 	if want, have := nextPod.UID, pl.GetScheduledPodUID(); want != have {
@@ -91,7 +91,7 @@ func Test_guestPool_bindingCycles(t *testing.T) {
 
 	status, _ = pl.Permit(ctx, nil, nextPod, "node")
 	if !status.IsSuccess() {
-		t.Fatalf("filter failed: %v", status)
+		t.Fatalf("filter failed: %v", status.Reasons())
 	}
 
 	if len(pl.GetBindingCycles()) != 2 {
@@ -121,13 +121,13 @@ func Test_guestPool_bindingCycles(t *testing.T) {
 	// nextPod is going to PreBind process.
 	status = pl.PreBind(ctx, nil, nextPod, "node")
 	if !status.IsSuccess() {
-		t.Fatalf("prebind failed: %v", status)
+		t.Fatalf("prebind failed: %v", status.Reasons())
 	}
 
 	// nextPod is going to Bind process.
 	status = pl.Bind(ctx, nil, nextPod, "node")
 	if !status.IsSuccess() {
-		t.Fatalf("bind failed: %v", status)
+		t.Fatalf("bind failed: %v", status.Reasons())
 	}
 
 	// nextPod is rejected in the binding cycle.
@@ -1109,7 +1109,7 @@ func TestPermit(t *testing.T) {
 			expectedStatusMessage: "name is bad",
 		},
 		{
-			name:                  "Error",
+			name:                  "Wait",
 			pod:                   test.PodSmall,
 			nodeName:              "wait",
 			expectedStatusCode:    framework.Wait,
@@ -1137,7 +1137,7 @@ func TestPermit(t *testing.T) {
 			guestURL:              test.URLErrorPanicOnPermit,
 			pod:                   test.PodSmall,
 			expectedStatusCode:    framework.Error,
-			expectedStatusMessage: "wasm: permit error: panic!\nwasm error: unreachable\nwasm stack trace:\n\tpanic_on_permit.$1() i32",
+			expectedStatusMessage: "wasm: permit error: panic!\nwasm error: unreachable\nwasm stack trace:\n\tpanic_on_permit.$1() i64",
 		},
 	}
 

scheduler/test/testdata/error/panic_on_permit.wat

@@ -14,7 +14,7 @@
   (data (i32.const 8) "panic!") ;; iovs[0]
 
   ;; On permit, write "panic!" to stdout and crash.
-  (func (export "permit") (result i32)
+  (func (export "permit") (result i64)
     ;; Write the panic to stdout via its iovec [offset, len].
     (call $wasi.fd_write
       (i32.const 1) ;; stdout
@@ -25,6 +25,5 @@
     drop ;; ignore the errno returned
 
     ;; Issue the unreachable instruction instead of returning a code
-    (unreachable)
-  )
+    (unreachable))
 )

scheduler/test/testdata/test/permit_from_global.wat

@@ -1,11 +1,30 @@
 ;; permit_from_global lets us test the value range of status_code
 (module $permit_from_global
 
+  ;; Allocate the minimum amount of memory, 1 page (64KB).
+  (memory (export "memory") 1 1)
+
   ;; status_code is set by the host.
   (global $status_code (export "status_code_global") (mut i32) (i32.const 0))
+  ;; timeout is set by the host.
+  (global $timeout (export "timeout_global") (mut i32) (i32.const 0))
 
-  ;; Allocate the minimum amount of memory, 1 page (64KB).
-  (memory (export "memory") 1 1)
+  (func (export "permit") (result i64)
+    ;; var status_code int32
+    (local $status_code i32)
+
+    ;; var timeout int32
+    (local $timeout i32)
+
+    ;; status_code = global.status_code
+    (local.set $status_code (global.get $status_code))
+
+    ;; timeout = global.timeout
+    (local.set $timeout (global.get $timeout))
 
-  (func (export "permit") (result i32) (return (global.get $status_code)))
+    ;; return uint64(timeout) << 32 | uint64(status_code)
+    (return
+      (i64.or
+        (i64.shl (i64.extend_i32_u (local.get $status_code)) (i64.const 32))
+        (i64.extend_i32_u (local.get $timeout)))))
 )

scheduler/test/testdata/test/postbind_from_global.wat

@@ -9,7 +9,7 @@
 
   (func (export "postbind")
     (if (i32.eq (global.get $flag) (i32.const 1))
-      (unreachable)
+      (then unreachable)
     )
   )
 

scheduler/test/testdata/test/reserve_from_global.wat

@@ -14,7 +14,7 @@
 
   (func (export "unreserve")
     (if (i32.eq (global.get $flag) (i32.const 1))
-      (unreachable)
+      (then unreachable)
     )
   )
 )