let v8 use libuv thread pool

[jiakai1000]

Is it possible to let v8 use libuv thread pool ? this could reduce extra thread numbers.

[mscdex]

If that were possible, doing so would further reduce the performance of fs, dns.lookup() (default method used internally by node), etc.

[jiakai1000]

@mscdex We can increase libuv thread number.
Also, doing so we can make thread pool load more balance.

[mscdex]

Sure, you can increase it, but I would guess most people use the default (currently 4).

[jiakai1000]

Well, and we also can increase default libuv thread number...

[mscdex]

I'm not 100% sure but I think 4 may have been chosen as that is/was the typical number of cores/cpus on most machines?

[jasnell]

While increasing the default will hopefully be something we can do at some point, 4 is still the most common average if I'm remembering correctly.

[hashseed]

In any case, having V8 use threads outside of the thread pool seems wrong. If 4 is the right default, you would in fact use more than 4 if V8 spins up its own threads. If you expect 4 + additional V8 threads to be a good number, then 4 is chosen too conservatively.

[mscdex]

@hashseed I'm not sure what the performance difference is (waiting for a libuv thread vs. OS scheduler), but if V8 were to use the libuv thread pool, some node requests would/could get blocked (even more so than they may be currently), whereas they may not have before.

[hashseed]

FWIW V8 hands over thread management to Chrome when embedded in Chrome.

[jiakai1000]

@hashseed Could you please explain the reason what Chrome did ?

[mscdex]

Node is quite a different thing than Chrome though ;-)

[hashseed]

@jeisinger probably knows more.

Iiuc V8 simply prefers to let the embedder take control. In case of Chrome, page start-up can be very busy wrt threading, and Chrome's scheduler likely has a better grasp than the OS scheduler.