diff --git a/README-zh.md b/README-zh.md
index 1776aa7..e094479 100644
--- a/README-zh.md
+++ b/README-zh.md
@@ -66,7 +66,9 @@ cargo test --workspace
 cargo fmt --check --all
 cargo clippy --workspace -- -D warnings
 
-# 运行基准测试（首次运行会生成约 5GB 测试文件）
+# 运行基准测试（需要先生成约 5GB 测试文件）
+mkdir -p /tmp/test-logviewer
+dd if=/dev/urandom of=/tmp/test-logviewer/extreme.log bs=1M count=5000
 cargo run -p log-viewer-bench
 cargo run -p log-viewer-bench -- --quick --suites startup,render --output results.md
 
@@ -102,4 +104,6 @@ CI 在 ubuntu-latest 和 windows-latest 上运行以下检查：
 
 自研基准测试框架，对比 mmap 与 pread 两种后端在 7 个测试场景（启动、渲染、跳转、内存、增长、轮转、并发）下的表现。使用挂钟计时和 `/proc/self/` 的 RSS 及页错误指标。结果以 Markdown 表格形式输出到 `benchmark-report.md`。
 
+基准测试框架要求 `/tmp/test-logviewer/extreme.log` 已经存在。它不会自动生成主用的 5GB 测试文件；请先使用上方的 `dd` 命令创建。
+
 基准测试二进制包含约 75 个单元测试，覆盖读取器后端和指标采集逻辑。
diff --git a/README.md b/README.md
index c89b788..59968a2 100644
--- a/README.md
+++ b/README.md
@@ -66,7 +66,9 @@ cargo test --workspace
 cargo fmt --check --all
 cargo clippy --workspace -- -D warnings
 
-# Run benchmarks (generates ~5GB test file on first run)
+# Run benchmarks (requires a pre-generated ~5GB test file)
+mkdir -p /tmp/test-logviewer
+dd if=/dev/urandom of=/tmp/test-logviewer/extreme.log bs=1M count=5000
 cargo run -p log-viewer-bench
 cargo run -p log-viewer-bench -- --quick --suites startup,render --output results.md
 
@@ -101,4 +103,6 @@ Planned but not yet built: filtering, bookmarks, sessions, search engine (stub m
 
 Custom harness comparing mmap vs pread backends across 7 suites (startup, render, jump, memory, growth, rotation, concurrent). Uses wall-clock timing with `/proc/self/` RSS and page fault metrics. Results are written as markdown tables to `benchmark-report.md`.
 
+The harness expects `/tmp/test-logviewer/extreme.log` to already exist. It does not generate the primary 5GB test file automatically; create it first with the `dd` command shown above.
+
 The benchmark binary includes ~75 unit tests for the reader backends and metrics collection.