Remove LIFO scheduler as Thread::yield during VT submission is a no-op

Author: franz1981

README.md

@@ -7,12 +7,12 @@ At a high level:
 - Each Netty event loop is backed by a virtual thread (the "event loop virtual thread").
 - Each such virtual thread is executed on a dedicated carrier platform thread.
 - Virtual threads created from the event-loop-specific ThreadFactory returned by the group will be associated with the same EventLoopScheduler and, when possible, will run on the same carrier platform thread as the event loop.
-- You can select FIFO or LIFO scheduling when constructing the group by passing `EventLoopSchedulerType` (default is FIFO).
+- You can select FIFO scheduling when constructing the group by passing `EventLoopSchedulerType` (default is FIFO).
 
 This allows code that must block (for example, blocking I/O or synchronous library calls) to be executed without moving work between unrelated threads, reducing wake-ups and improving cache locality compared to offloading to an external thread pool.
 
 ## Key behavior (user-facing)
-- Create a `VirtualMultithreadIoEventLoopGroup` like any other Netty `EventLoopGroup`. It behaves like a `MultiThreadIoEventLoopGroup` from the Netty API, but the event loops are driven by virtual threads and coordinated with carrier platform threads by a per-event-loop `EventLoopScheduler` (FIFO or LIFO).
+- Create a `VirtualMultithreadIoEventLoopGroup` like any other Netty `EventLoopGroup`. It behaves like a `MultiThreadIoEventLoopGroup` from the Netty API, but the event loops are driven by virtual threads and coordinated with carrier platform threads by a per-event-loop `EventLoopScheduler` (FIFO).
 - Call `group.vThreadFactory()` to obtain a `ThreadFactory` that creates virtual threads tied to an `EventLoopScheduler` of the group. When those virtual threads block, the scheduler parks them and resumes them later using the carrier thread.
 - Virtual threads created via the group's `vThreadFactory()` will attempt to inherit the scheduler and run with low-overhead handoffs back to the event loop when continuing work.
 - Virtual threads created with `Thread.ofVirtual().factory()` (the JVM default factory) do NOT automatically inherit the group's scheduler.

benchmark-runner/README.md

@@ -66,7 +66,6 @@ All configuration is via environment variables:
 | `SERVER_THREADS` | 2 | Number of event loop threads |
 | `SERVER_REACTIVE` | false | Use reactive handler with Reactor |
 | `SERVER_USE_CUSTOM_SCHEDULER` | false | Use custom Netty scheduler |
-| `SERVER_SCHEDULER_TYPE` | fifo | Scheduler type: fifo or lifo |
 | `SERVER_IO` | epoll | I/O type: epoll, nio, or io_uring |
 | `SERVER_NO_TIMEOUT` | false | Disable HTTP client timeout |
 | `SERVER_TASKSET` | 2,3 | CPU affinity (e.g., "2-5") |
@@ -277,7 +276,6 @@ java \
   --mock-url http://localhost:8080/fruits \
   --threads 2 \
   --use-custom-scheduler true \
-  --scheduler-type fifo \
   --io epoll
 ```
 

benchmark-runner/scripts/run-benchmark.sh

@@ -31,7 +31,6 @@ MOCK_TASKSET="${MOCK_TASKSET:-4,5}"  # CPUs for mock server
 SERVER_PORT="${SERVER_PORT:-8081}"
 SERVER_THREADS="${SERVER_THREADS:-2}"
 SERVER_USE_CUSTOM_SCHEDULER="${SERVER_USE_CUSTOM_SCHEDULER:-false}"
-SERVER_SCHEDULER_TYPE="${SERVER_SCHEDULER_TYPE:-fifo}"
 SERVER_IO="${SERVER_IO:-epoll}"
 SERVER_TASKSET="${SERVER_TASKSET:-2,3}"  # CPUs for handoff server
 SERVER_JVM_ARGS="${SERVER_JVM_ARGS:-}"
@@ -52,7 +51,7 @@ LOAD_GEN_URL="${LOAD_GEN_URL:-http://localhost:8081/fruits}"
 WARMUP_DURATION="${WARMUP_DURATION:-10s}"
 TOTAL_DURATION="${TOTAL_DURATION:-30s}"
 MIN_STEADY_STATE_SECONDS=20
-PROFILING_DELAY_SECONDS="${PROFILING_DELAY_SECONDS:-5}"
+PROFILING_DELAY_SECONDS="${PROFILING_DELAY_SECONDS:-10}"
 PROFILING_DURATION_SECONDS="${PROFILING_DURATION_SECONDS:-10}"
 
 # Profiling configuration
@@ -409,7 +408,6 @@ start_handoff_server() {
         --mock-url http://localhost:$MOCK_PORT/fruits \
         --threads $SERVER_THREADS \
         --use-custom-scheduler $SERVER_USE_CUSTOM_SCHEDULER \
-        --scheduler-type $SERVER_SCHEDULER_TYPE \
         --io $SERVER_IO \
         --no-timeout $SERVER_NO_TIMEOUT \
         --reactive $SERVER_REACTIVE \
@@ -704,7 +702,6 @@ print_config() {
     log "  Threads:        $SERVER_THREADS"
     log "  Reactive:       $SERVER_REACTIVE"
     log "  Custom Sched:   $SERVER_USE_CUSTOM_SCHEDULER"
-    log "  Scheduler Type: $SERVER_SCHEDULER_TYPE"
     log "  I/O Type:       $SERVER_IO"
     log "  No Timeout:     $SERVER_NO_TIMEOUT"
     log "  Poller Mode:    $SERVER_POLLER_MODE"
@@ -791,7 +788,6 @@ Handoff Server:
   SERVER_THREADS            Number of event loop threads (default: 2)
   SERVER_REACTIVE           Use reactive handler with Reactor (default: false)
   SERVER_USE_CUSTOM_SCHEDULER  Use custom Netty scheduler (default: false)
-  SERVER_SCHEDULER_TYPE     Scheduler type: fifo or lifo (default: fifo)
   SERVER_IO                 I/O type: epoll, nio, or io_uring (default: epoll)
   SERVER_NO_TIMEOUT         Disable HTTP client timeout (default: false)
   SERVER_TASKSET            CPU affinity range (default: "2,3")

benchmark-runner/src/main/java/io/netty/loom/benchmark/runner/HandoffHttpServer.java

@@ -381,7 +381,7 @@ private static void printUsage() {
 						  --mock-url <url>               Mock server URL (default: http://localhost:8080/fruits)
 						  --threads <n>                  Number of event loop threads (default: 1)
 						  --use-custom-scheduler <bool>  Use custom Netty scheduler (default: false, ignored if --reactive is true)
-						  --scheduler-type <fifo|lifo>   Scheduler type for custom scheduler (default: fifo)
+						  --scheduler-type <fifo>        Scheduler type for custom scheduler (default: fifo)
 						  --io <epoll|nio|io_uring>      I/O type (default: epoll)
 						  --no-timeout <true|false>      Disable HTTP client timeout (default: false)
 						  --reactive <true|false>        Use reactive handler with Reactor (default: false)

core/src/main/java/io/netty/loom/EventLoopSchedulerType.java

@@ -15,5 +15,5 @@
 package io.netty.loom;
 
 public enum EventLoopSchedulerType {
-	FIFO, LIFO
+	FIFO
 }