runtime: usleep before stealing runnext only if not in syscall

In the scheduler's steal path, we usleep(3) before stealing a _Prunning
P's runnext slot. Before CL 646198, we would not call usleep(3) if the P
was in _Psyscall. After CL 646198, Ps with Gs in syscalls stay in
_Prunning until stolen, meaning we might unnecessarily usleep(3) where
we didn't before. This probably isn't a huge deal in most cases, but can
cause some apparent slowdowns in microbenchmarks that frequently take
the steal path while there are syscalling goroutines.

Change-Id: I5bf3df10fe61cf8d7f0e9fe9522102de66faf344
Reviewed-on: https://go-review.googlesource.com/c/go/+/720441
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
1 file changed
tree: b4c0d3dba5c11671d8d0958901871e523885fde9
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. codereview.cfg
  11. CONTRIBUTING.md
  12. go.env
  13. LICENSE
  14. PATENTS
  15. README.md
  16. SECURITY.md
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