From 9e5ea67e268be2659cd30ebaed7044d298198ab0 Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Sat, 23 Apr 2016 21:14:49 +0100
Subject: 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
---
 rts/posix/OSThreads.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

(limited to 'rts/posix/OSThreads.c')

diff --git a/rts/posix/OSThreads.c b/rts/posix/OSThreads.c
index ad138d314d..72538c1bf3 100644
--- a/rts/posix/OSThreads.c
+++ b/rts/posix/OSThreads.c
@@ -70,6 +70,10 @@
 # include <signal.h>
 #endif
 
+#ifdef HAVE_NUMA_H
+#include <numa.h>
+#endif
+
 /*
  * This (allegedly) OS threads independent layer was initially
  * abstracted away from code that used Pthreads, so the functions
@@ -308,10 +312,32 @@ setThreadAffinity(uint32_t n, uint32_t m)
 
 #else
 void
-setThreadAffinity (uint32_t n GNUC3_ATTRIBUTE(__unused__),
-                   uint32_t m GNUC3_ATTRIBUTE(__unused__))
+setThreadAffinity (uint32_t n STG_UNUSED,
+                   uint32_t m STG_UNUSED)
+{
+}
+#endif
+
+#ifdef HAVE_NUMA_H
+void setThreadNode (uint32_t node)
 {
+    ASSERT(node < RtsFlags.GcFlags.nNumaNodes);
+    if (numa_run_on_node(node) == -1) {
+        sysErrorBelch("numa_run_on_node");
+        stg_exit(1);
+    }
+}
+
+void releaseThreadNode (void)
+{
+    if (numa_run_on_node(-1) == -1) {
+        sysErrorBelch("numa_run_on_node");
+        stg_exit(1);
+    }
 }
+#else
+void setThreadNode (uint32_t node STG_UNUSED) { /* nothing */ }
+void releaseThreadNode (void) { /* nothing */ }
 #endif
 
 void
-- 
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