gulp-typescript: gulp-typescript substantially slower than tsc

I realize this is a bit of a vague issue, but I’d really love to get some ideas how I could speed this up. I have an existing build that I’m adding TypeScript to, and noticing substantial performance differences between compiling with gulp-typescript vs. tsc. The actual numbers:

time tsc
tsc  1.65s user 0.07s system 139% cpu 1.232 total

time gulp compile:typescript
gulp compile:typescript  6.25s user 0.92s system 116% cpu 6.134 total

The gulp task is pretty minimal:

const gulp = require('gulp')
const typescript = require('gulp-typescript')
const tsProject = typescript.createProject('tsconfig.json', {
  typescript: require('typescript')
})
gulp.task('compile:typescript', function() {
  return tsProject.src()
    .pipe(typescript(tsProject)).js
    .pipe(gulp.dest('app'))
})

As is the tsconfig.json

{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "sourceMap": false,
    "outDir": "app",
    "rootDir": "server-src",
    "noImplicitAny": true
  },
  "exclude": [
    ".git",
    "node_modules",
    "typings/browser.d.ts",
    "typings/browser",
    "typings/main",
  ]
}

Some random other stuff that could potentially be contributing:

• As I mentioned I’m adding TypeScript to an existing project. The source directory contains a lot of es6 files with .js extensions, but only a couple of TypeScript files.
  • I would hope that using tsProject and the same tsconfig.json would ensure they’re scanning the same files though, and I’ve monitored the build dir with fswatch and confirmed that both tsc and gulp compile:typescript are writing the same set of output files.