runtime: threadcreate profile is broken

[dvyukov]

With the new scheduler threadcreate profile is broken. Most of the threads are created
by sysmon thread, which stack is not very informative.
We need to either remove the profile, or capture stack of the blocking cgo/syscall that
caused new thread creation.

[rsc]

Comment 1:

It would be nice to capture a useful stack but it may be okay to remove it
too. I can't remember ever using it.

[dvyukov]

Comment 2:

What is a "useful stack"?
I've attached threadcreate profile from HTTP server FTR.
Lots of threads are created by sysmon (not useful).
Timerproc created 3 threads (not useful).
Creation of random goroutines caused thread creation up to GOMAXPROCS (not useful).
I can imagine an end user trying to figure out what threadcreate profile is trying to
say...
It must be centered around blocking syscalls and locked threads. But which exactly?
Probably all, because they all can trigger thread creation. It all needs to be rethought
and probably even renamed.
Probably now it's better to just remove it.

Attachments:

1. threadcreate.txt (5407 bytes)

[rsc]

Comment 3:

The idea was that if, for example, your program was creating 1000s of
threads because they kept getting blocked on cgo DNS lookups, you'd see the
cgo DNS call in the profile sample, because it is what blocked and
triggered the creation of a new thread.

[robpike]

Comment 4:

Not for 1.2.

Labels changed: removed go1.2maybe.

[rsc]

Comment 5:

Labels changed: added go1.3maybe.

[rsc]

Comment 6:

Labels changed: removed feature.

[rsc]

Comment 7:

Labels changed: added release-none, removed go1.3maybe.

[rsc]

Comment 8:

Labels changed: added repo-main.