From 541ad0a2ca7a82ebc4f80f18d5ff669872f97e63 Mon Sep 17 00:00:00 2001
From: Yuxuan Zhang <github@z-yx.cc>
Date: Sat, 30 Dec 2023 11:15:00 -0500
Subject: [PATCH] cleanup logic, improve perf

---
 src/node/build/render-worker.ts | 14 ++++++++++----
 src/node/siteConfig.ts          |  2 +-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/node/build/render-worker.ts b/src/node/build/render-worker.ts
index 04ce2773..8f8c890d 100644
--- a/src/node/build/render-worker.ts
+++ b/src/node/build/render-worker.ts
@@ -12,7 +12,14 @@ export default async function cluster(
   pages: string[],
   update: UpdateHandle
 ) {
-  const concurrency = context.config.buildConcurrency || 1
+  // - Each render worker could consume up to 150% of a CPU core.
+  // - One extra core is allocated to the main thread.
+  // - Excess worker will cause too much RPC workload for main thread,
+  //   therefore harm the overall performance.
+  const concurrency = Math.round(
+    Math.max((context.config.buildConcurrency - 1) / 1.5, 1)
+  )
+
   const num_tasks = pages.length
 
   const pageAlloc: TaskAllocator<string> = async () => {
@@ -52,12 +59,10 @@ async function renderWorker() {
   const ctx = new RpcContext(parentPort!)
   try {
     const {
-      concurrency,
       entryPath,
       pageAlloc,
       context
     }: {
-      concurrency: number
       entryPath: string
       pageAlloc: TaskAllocator<string>
       context: RenderPageContext
@@ -72,7 +77,8 @@ async function renderWorker() {
         await renderPage(render, page, context)
       }
     }
-    await Promise.all(Array.from({ length: concurrency * 4 }, () => executor()))
+    const concurrency = Math.max(context.config.buildConcurrency, 1)
+    await Promise.all(Array.from({ length: concurrency }, () => executor()))
   } catch (e) {
     console.error(e)
   } finally {
diff --git a/src/node/siteConfig.ts b/src/node/siteConfig.ts
index 21b99bce..92bae1d0 100644
--- a/src/node/siteConfig.ts
+++ b/src/node/siteConfig.ts
@@ -152,7 +152,7 @@ export interface UserConfig<ThemeConfig = any>
    * A lower number will reduce the memory usage but will increase the build time.
    *
    * @experimental
-   * @default 64
+   * @default "Number of CPU cores available"
    */
   buildConcurrency?: number