Add a brief description of each benchmark.

README.md

@@ -7,6 +7,8 @@ The primary required setup is to provide a folder with a `retries` file and a `t
 is gathered into https://github.com/rust-lang-nursery/rustc-timing by Rust Infrastructure; cloning
 that is the best approach for working on the frontend.
 
-Additional documentation on running and setting up the frontend and backend can be found in README
-files in the `collector` and `site` directories.
+Additional documentation on running and setting up the frontend and backend can
+be found in the `README` files in the `collector` and `site` directories.
 
+Additional documentation on the benchmark programs can be found in the `README`
+file in the `collector/benchmarks` directory.

collector/README.md

@@ -1,5 +1,10 @@
 # Rust Compiler Performance Benchmarking and Profiling
 
+## The benchmarks
+
+The individual benchmarks are described in the `README` file in the
+`collector/benchmarks` directory.
+
 ## How to build
 
 Before doing anything else, you should build `collector` (for running the

collector/benchmarks/README.md

@@ -0,0 +1,90 @@
+# The Benchmark Suite
+
+This file describes the programs in the benchmark suite and explains why they
+were included.
+
+## Real programs that are important
+
+These are real programs that are important in some way, and worth tracking.
+
+- **cargo**: The Rust package manager. An important program in the Rust
+  ecosystem.
+- **clap-rs**: A command line argument parser. A crate used by many Rust
+  programs.
+- **cranelift-codegen**: The largest crate from a code generator. Used by
+  Firefox.
+- **crates.io**: Source code for `crates.io`. An important site in the
+  Rust ecosystem.
+- **futures**: A futures implementation. Used by many Rust programs.
+- **helloworld**: A trivial program. Gives a lower bound on compile time.
+- **hyper**: An HTTP library. An important part of the Rust ecosystem.
+- **piston-image**: A modular game engine. An interesting Rust program.
+- **regex**: A regular expression parser. Used by many Rust programs.
+- **ripgrep**: A line-oriented search tool. A widely-used utility.
+- **script-servo**: Servo's `script` crate. A particularly large crate.
+- **serde**: A serialization/deserialization crate. Used by many other
+  Rust programs.
+- **style-servo**: Servo's `style` crate. A large crate, and one used by
+  Firefox.
+- **syn**: A library for parsing Rust code. An important part of the Rust
+  ecosystem.
+- **tokio-webpush-simple**: A simple web server built with tokio. Uses futures
+  a lot.
+- **webrender**: A web renderer. Used by Firefox and Servo.
+
+## Real programs that stress the compiler
+
+These are real programs that are known to stress the compiler in interesting
+ways.
+
+- **encoding**: Character encoding support. Contains some large tables.
+- **html5ever**: An HTML parser. Stresses macro parsing code significantly.
+- **inflate**: An old implementation of the DEFLATE algorithm. Stresses the
+  compiler in certain ways.
+- **keccak**: A cryptography algorithm. Contains a very high number of locals
+  and basic blocks.
+- **packed-simd**: Portable packed SIMD vectors. Exercises SIMD features
+  heavily, and uses a compiler plugin.
+- **sentry-cli**: A command line utility.
+  [Reported](https://github.com/rust-lang-nursery/rustc-perf/issues/232#issuecomment-391439420)
+  as being slow to compile.
+- **ucd**: A Unicode crate. Contains large statics that
+  [stress](https://github.com/rust-lang/rust/issues/53643) the borrow checker's
+  implementation of NLL.
+- **unicode_normalization**: Unicode character composition and decomposition
+  utilities. Uses huge `match` statements that stress the compiler in unusual
+  ways.
+- **wg-grammar**: A parser generator.
+  [Stresses](https://github.com/rust-lang/rust/issues/58178) the borrow
+  checker's implementation of NLL.
+
+## Artificial stress tests
+
+These are artificial programs that stress one particular aspect of the
+compiler. Some are entirely artificial, and some are extracted from real
+programs.
+
+- **coercions**: Contains a static array with 65,536 string literals, which
+  caused [poor performance](https://github.com/rust-lang/rust/issues/32278) in
+  the past.
+- **ctfe-stress-2**: A stress test for compile-time function evaluation.
+- **deeply-nested**: A small program that caused [exponential
+  behavior](https://github.com/rust-lang/rust/issues/38528) in the past.
+- **deep-vector**: A test containing a single large vector of zeroes, which
+  caused [poor performance](https://github.com/rust-lang/rust/issues/20936) in
+  the past.
+- **issue-46449**: A small program that caused [poor
+  performance](https://github.com/rust-lang/rust/issues/46449) in the past.
+- **regression-31157**: A small program that caused a [large performance
+  regression](https://github.com/rust-lang/rust/issues/31157) from the past.
+- **tuple-stress**: Contains a single array of 65,535 nested `(i32, (f64, f64,
+  f64))` tuples. The data was extracted and reduced from a [program dealing
+  with grid coordinates](https://github.com/urschrei/ostn15_phf) that was
+  causing rustc to [run out of
+  memory](https://github.com/rust-lang/rust/issues/36799).
+- **unify-linearly**: Contains many variables that all have equality relations
+  between them, which caused [exponential
+  behavior](https://github.com/rust-lang/rust/pull/32062) in the past.
+- **unused-warnings**: Contains many unused imports, which caused [quadratic
+  behavior](https://github.com/rust-lang/rust/issues/43572) in the past.
+