async.js

var buf = require('crypto').randomBytes(1024);
var zlib = require('zlib');
function doNothing() {}
var count = process.argv[2] || 1;

for (var i = 0; i < count; i++) {
  zlib.deflate(buf, doNothing);
}

sync.js

var buf = require('crypto').randomBytes(1024);
var zlib = require('zlib');
var count = process.argv[2] || 1;

for (var i = 0; i < count; i++) {
  var inf = zlib.deflateSync(buf);
}

time

drkoljan@ns396737:~$ time node/node test-zlib/sync.js 1

real    0m0.063s
user    0m0.056s
sys     0m0.004s
drkoljan@ns396737:~$ time node/node test-zlib/async.js 1

real    0m0.066s
user    0m0.048s
sys     0m0.016s
drkoljan@ns396737:~$ time node/node test-zlib/sync.js 100

real    0m0.078s
user    0m0.064s
sys     0m0.012s
drkoljan@ns396737:~$ time node/node test-zlib/async.js 100

real    0m0.101s
user    0m0.112s
sys     0m0.008s
drkoljan@ns396737:~$ time node/node test-zlib/sync.js 10000

real    0m0.911s
user    0m0.856s
sys     0m0.072s
drkoljan@ns396737:~$ time node/node test-zlib/async.js 10000

real    0m1.751s
user    0m2.032s
sys     0m0.336s
drkoljan@ns396737:~$ time node/node test-zlib/sync.js 100000

real    0m9.147s
user    0m8.816s
sys     0m0.364s
drkoljan@ns396737:~$ time node/node test-zlib/async.js 100000

real    0m18.142s
user    0m20.964s
sys     0m3.332s