Address review feedback

1 files changed, 16 insertions, 9 deletions

diff --git a/src/doc/rustc-dev-guide/src/tests/intro.md b/src/doc/rustc-dev-guide/src/tests/intro.md
index 034b7aac1c5..f4164de5ee6 100644
--- a/src/doc/rustc-dev-guide/src/tests/intro.md
+++ b/src/doc/rustc-dev-guide/src/tests/intro.md
@@ -171,9 +171,10 @@ communicate with the server to coordinate running tests (see
 ## Crater
 
 [Crater](https://github.com/rust-lang-nursery/crater) is a tool for compiling
-and running tests for _every_ crate on [crates.io](https://crates.io/). It is
-mainly used for checking for extent of breakage when implementing potentially
-breaking changes.
+and running tests for _every_ crate on [crates.io](https://crates.io/) (and a
+few on GitHub). It is mainly used for checking for extent of breakage when
+implementing potentially breaking changes and ensuring lack of breakage by
+running beta vs stable compiler versions.
 
 ### When to run Crater
 
@@ -184,9 +185,16 @@ or could cause breakage. If you are unsure, feel free to ask your PR's reviewer.
 
 The rust team maintains a few machines that can be used for running crater runs
 on the changes introduced by a PR. If your PR needs a crater run, leave a
-comment for the triage team in the PR thread. Your will be enqueued by the
-triage team and the results will be posted when they are ready. A crater run
-usually takes a few days (as of this writing).
+comment for the triage team in the PR thread. Please inform the team whether
+you require a "check-only" crater run, a "build only" crater run, or a
+"build-and-test" crater run. The difference is primarily in time; the
+conservative (if you're not sure) option is to go for the build-and-test run.
+If making changes that will only have an effect at compile-time (e.g.,
+implementing a new trait) then you only need a check run.
+
+Your PR will be enqueued by the triage team and the results will be posted when
+they are ready. Check runs will take around ~3-4 days, with the other two
+taking 5-6 days on average.
 
 While crater is really useful, it is also important to be aware of a few caveats:
 
@@ -195,9 +203,8 @@ While crater is really useful, it is also important to be aware of a few caveats
   successful crater run is not a magically green light that there will be no
   breakage; you still need to be careful.
 
-- Crater only runs Linux builds (on x86_64, I believe). Thus, other
-  architectures and platforms are not tested. Critically, this includes
-  Windows.
+- Crater only runs Linux builds on x86_64. Thus, other architectures and
+  platforms are not tested. Critically, this includes Windows.
 
 - Many crates are not tested. This could be for a lot of reasons, including
   that the crate doesn't compile any more (e.g. used old nightly features),