Please find attached the startup trace  (headless_shell is run in the following way headless_shell --trace-startup --trace-startup-file=/tmp/trace_5s.json  --trace-startup-duration=5 --no-sandbox --remote-debugging-port=9222)

Deleted: trace_5s.json 5.6 MB

trace_5s.json 5.6 MB View Download

Hmm, that trace looks very different from mine (attached). In particular sandbox setup and GPU process initialization seem to take a lot of time. This isn't a debug build, is it?

I made a quick script measuring the connection time and ran it like this:

mkdir -p /tmp/h; for i in $(seq 1 10); do rm -f /tmp/h/DevToolsActivePort; ~/code/chromium/src/out_linux/Release/headless_shell --user-data-dir=/tmp/h --remote-debugging-port=9222 > /dev/null 2>&1 & time inotifywait -qqt 15 -e create -e moved_to /tmp/h; node startup-test.js; kill $!; done

On my machine (HP Z620) total startup time is about 500ms in total, 440ms of which is spent waiting for DevToolsActivePort to get created and 60ms is the time to connect to the socket.

Deleted: trace_5s.json 373 KB

trace_5s.json 373 KB View Download

Deleted: startup-test.js 320 bytes

startup-test.js 320 bytes View Download

The build is not a debug one. It is build with the following arg :
import("//build/args/headless.gn")
is_debug = false 
is_component_build = true
symbol_level = 0
enable_nacl = false
remove_webcore_debug_symbols = true

I have found a way around, when i change the build paramater is_component_build to False, all is working as expected (no long delay to connect to DevTool).

Interesting, I'm not sure why a component build would have such a huge effect, but in general non-component builds are recommended for best performance.