async-llvm(24): Improve scheduling and documentation.

src/Cargo.lock

@@ -1517,11 +1517,11 @@ dependencies = [
 name = "rustc_trans"
 version = "0.0.0"
 dependencies = [
- "crossbeam 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "flate2 0.2.19 (registry+https://github.com/rust-lang/crates.io-index)",
  "gcc 0.3.51 (registry+https://github.com/rust-lang/crates.io-index)",
  "jobserver 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num_cpus 1.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "owning_ref 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc 0.0.0",
  "rustc-demangle 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",

src/librustc_trans/Cargo.toml

@@ -10,7 +10,7 @@ crate-type = ["dylib"]
 test = false
 
 [dependencies]
-crossbeam = "0.2"
+num_cpus = "1.0"
 flate2 = "0.2"
 jobserver = "0.1.5"
 log = "0.3"

src/librustc_trans/base.rs

@@ -80,6 +80,7 @@
 use std::ffi::{CStr, CString};
 use std::str;
 use std::sync::Arc;
+use std::time::Instant;
 use std::i32;
 use syntax_pos::Span;
 use syntax::attr;
@@ -1082,10 +1083,22 @@ pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let mut all_stats = Stats::default();
     let mut module_dispositions = tcx.sess.opts.incremental.as_ref().map(|_| Vec::new());
 
+    // We sort the codegen units by size. This way we can schedule work for LLVM
+    // a bit more efficiently. Note that "size" is defined rather crudely at the
+    // moment as it is just the number of TransItems in the CGU, not taking into
+    // account the size of each TransItem.
+    let codegen_units = {
+        let mut codegen_units = codegen_units;
+        codegen_units.sort_by_key(|cgu| -(cgu.items().len() as isize));
+        codegen_units
+    };
+
     for (cgu_index, cgu) in codegen_units.into_iter().enumerate() {
         ongoing_translation.wait_for_signal_to_translate_item();
         ongoing_translation.check_for_errors(tcx.sess);
 
+        let start_time = Instant::now();
+
         let module = {
             let _timing_guard = time_graph
                 .as_ref()
@@ -1108,10 +1121,18 @@ pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             module
         };
 
+        let time_to_translate = Instant::now().duration_since(start_time);
+
+        // We assume that the cost to run LLVM on a CGU is proportional to
+        // the time we needed for translating it.
+        let cost = time_to_translate.as_secs() * 1_000_000_000 +
+                   time_to_translate.subsec_nanos() as u64;
+
         let is_last_cgu = (cgu_index + 1) == codegen_unit_count;
 
         ongoing_translation.submit_translated_module_to_llvm(tcx.sess,
                                                              module,
+                                                             cost,
                                                              is_last_cgu);
         ongoing_translation.check_for_errors(tcx.sess);
     }

src/librustc_trans/lib.rs

@@ -39,7 +39,6 @@
 use std::sync::Arc;
 
 extern crate flate2;
-extern crate crossbeam;
 extern crate libc;
 extern crate owning_ref;
 #[macro_use] extern crate rustc;
@@ -55,6 +54,7 @@
 extern crate rustc_bitflags;
 extern crate rustc_demangle;
 extern crate jobserver;
+extern crate num_cpus;
 
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;