NUMA support

Summary:
The aim here is to reduce the number of remote memory accesses on
systems with a NUMA memory architecture, typically multi-socket servers.

Linux provides a NUMA API for doing two things:
* Allocating memory local to a particular node
* Binding a thread to a particular node

When given the +RTS --numa flag, the runtime will
* Determine the number of NUMA nodes (N) by querying the OS
* Assign capabilities to nodes, so cap C is on node C%N
* Bind worker threads on a capability to the correct node
* Keep a separate free lists in the block layer for each node
* Allocate the nursery for a capability from node-local memory
* Allocate blocks in the GC from node-local memory

For example, using nofib/parallel/queens on a 24-core 2-socket machine:

```
$ ./Main 15 +RTS -N24 -s -A64m
  Total   time  173.960s  (  7.467s elapsed)

$ ./Main 15 +RTS -N24 -s -A64m --numa
  Total   time  150.836s  (  6.423s elapsed)
```

The biggest win here is expected to be allocating from node-local
memory, so that means programs using a large -A value (as here).

According to perf, on this program the number of remote memory accesses
were reduced by more than 50% by using `--numa`.

Test Plan:
* validate
* There's a new flag --debug-numa=<n> that pretends to do NUMA without
  actually making the OS calls, which is useful for testing the code
  on non-NUMA systems.
* TODO: I need to add some unit tests

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

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2199

1 files changed, 5 insertions, 1 deletions

diff --git a/includes/RtsAPI.h b/includes/RtsAPI.h
index a4a094fd14..230c982c12 100644
--- a/includes/RtsAPI.h
+++ b/includes/RtsAPI.h
@@ -179,7 +179,11 @@ Capability *rts_unsafeGetMyCapability (void);
 // Note that the thread may still be migrated by the RTS scheduler, but that
 // will only happen if there are multiple threads running on one Capability and
 // another Capability is free.
-void setInCallCapability (int preferred_capability);
+//
+// If affinity is non-zero, the current thread will be bound to
+// specific CPUs according to the prevailing affinity policy for the
+// specified capability, set by either +RTS -qa or +RTS --numa.
+void rts_setInCallCapability (int preferred_capability, int affinity);
 
 /* ----------------------------------------------------------------------------
    Building Haskell objects from C datatypes.