Overhaul GC stats

Summary:
Visible API changes:

* The C struct `GCDetails` gives the stats about a single GC.  This is
  passed to the `gcDone()` callback if one is set via the
  RtsConfig. (previously we just passed a collection of values, so this
  is more extensible, at the expense of breaking the existing API)

* `RTSStats` gives cumulative stats since the start of the program,
  and includes the `GCDetails` for the most recent GC.  This struct
  can be obtained via `getRTSStats()` (the old `getGCStats()` has been
  removed, and `getGCStatsEnabled()` has been renamed to
  `getRTSStatsEnabled()`)

Improvements:

* The per-GC stats and cumulative stats are now cleanly separated.

* Inside the RTS we have a top-level `RTSStats` struct to keep all our
  stats in, previously this was just a collection of strangely-named
  variables.  This struct is mostly just copied in `getRTSStats()`, so
  the implementation of that function is a lot shorter.

* Types are more consistent.  We use a uint64_t byte count for all
  memory values, and Time for all time values.

* Names are more consistent.  We use a suffix `_bytes` for all byte
  counts and `_ns` for all time values.

* We now collect information about the amount of memory in large
  objects and compact objects in `GCDetails`. (the latter was the reason
  I started doing this patch but it seems to have ballooned a bit!)

* I fixed a bug in the calculation of the elapsed MUT time, and added
  an ASSERT to stop the calculations going wrong in the future.

For now I kept the Haskell API in `GHC.Stats` the same, by
impedence-matching with the new API.  We could either break that API
and make it match the C API more closely, or we could add a new API
and deprecate the old one.  Opinions welcome.

This stuff is very easy to get wrong, and it's hard to test.  Reviews
welcome!

Test Plan:
manual testing
validate

Reviewers: bgamari, niteria, austin, ezyang, hvr, erikd, rwbarton, Phyx

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2756

1 files changed, 2 insertions, 5 deletions

diff --git a/rts/sm/GC.c b/rts/sm/GC.c
index ea80d6dec1..c41c9791dc 100644
--- a/rts/sm/GC.c
+++ b/rts/sm/GC.c
@@ -187,7 +187,7 @@ GarbageCollect (uint32_t collect_gen,
 {
   bdescr *bd;
   generation *gen;
-  StgWord live_blocks, live_words, par_max_copied, par_tot_copied;
+  StgWord live_blocks, live_words, par_max_copied;
 #if defined(THREADED_RTS)
   gc_thread *saved_gct;
 #endif
@@ -459,7 +459,6 @@ GarbageCollect (uint32_t collect_gen,
 
   copied = 0;
   par_max_copied = 0;
-  par_tot_copied = 0;
   {
       uint32_t i;
       for (i=0; i < n_gc_threads; i++) {
@@ -474,10 +473,8 @@ GarbageCollect (uint32_t collect_gen,
           copied += gc_threads[i]->copied;
           par_max_copied = stg_max(gc_threads[i]->copied, par_max_copied);
       }
-      par_tot_copied = copied;
       if (n_gc_threads == 1) {
           par_max_copied = 0;
-          par_tot_copied = 0;
       }
   }
 
@@ -773,7 +770,7 @@ GarbageCollect (uint32_t collect_gen,
   // ok, GC over: tell the stats department what happened.
   stat_endGC(cap, gct, live_words, copied,
              live_blocks * BLOCK_SIZE_W - live_words /* slop */,
-             N, n_gc_threads, par_max_copied, par_tot_copied);
+             N, n_gc_threads, par_max_copied);
 
 #if defined(RTS_USER_SIGNALS)
   if (RtsFlags.MiscFlags.install_signal_handlers) {