[Git][ghc/ghc][wip/T25459] rts: Increase gen_workspace alignment to 128 bytes on AArch64

[Ben Gamari (@bgamari)]

Ben Gamari pushed to branch wip/T25459 at Glasgow Haskell Compiler / GHC


Commits:
3da67f40 by Ben Gamari at 2024-11-15T10:53:09-05:00
rts: Increase gen_workspace alignment to 128 bytes on AArch64

Increase to match the 128-byte cache-line size of Apple's ARMv8
implementation.

Closes #25459.

- - - - -


5 changed files:

- rts/Capability.h
- rts/include/rts/Config.h
- rts/include/rts/storage/HeapAlloc.h
- rts/sm/GC.c
- rts/sm/GCThread.h


Changes:

=====================================
rts/Capability.h
=====================================
@@ -29,11 +29,7 @@
 
 // We never want a Capability to overlap a cache line with
 // anything else, so round it up to a cache line size:
-#if defined(s390x_HOST_ARCH)
-#define CAPABILITY_ALIGNMENT 256
-#else
-#define CAPABILITY_ALIGNMENT 64
-#endif
+#define CAPABILITY_ALIGNMENT CACHELINE_SIZE
 
 /* A forward declaration of the per-capability data structures belonging to
  * the I/O manager. It is opaque and only passed by pointer, so the full


=====================================
rts/include/rts/Config.h
=====================================
@@ -82,3 +82,19 @@ code.
 #else
 #define MAX_N_CAPABILITIES 1
 #endif
+
+// The host's cacheline size.
+// We use 128-bytes here on AArch64 as this is the cache-line size of new Apple
+// ARMv8 platforms.
+//
+// At some point we may want to determine this via `configure`.
+#if defined(s390x_HOST_ARCH)
+#define CACHELINE_SIZE 256
+#elif defined(aarch64_HOST_ARCH)
+#define CACHELINE_SIZE 128
+#elif defined(x86_64_HOST_ARCH)
+#define CACHELINE_SIZE 64
+#else
+#define CACHELINE_SIZE 64
+#endif
+


=====================================
rts/include/rts/storage/HeapAlloc.h
=====================================
@@ -59,7 +59,7 @@ extern SpinLock gc_alloc_block_sync;
 struct mblock_address_range {
     W_ begin, end;
     W_ padding[6];  // ensure nothing else inhabits this cache line
-} ATTRIBUTE_ALIGNED(64);
+} ATTRIBUTE_ALIGNED(CACHELINE_SIZE);
 extern struct mblock_address_range mblock_address_space;
 
 # define HEAP_ALLOCED(p)        ((W_)(p) >= mblock_address_space.begin && \


=====================================
rts/sm/GC.c
=====================================
@@ -153,9 +153,9 @@ static Condition gc_exit_arrived_cv;
 static Condition gc_exit_leave_now_cv;
 
 #else // THREADED_RTS
-// Must be aligned to 64-bytes to meet stated 64-byte alignment of gen_workspace
+// Must match the alignment of gen_workspace.
 StgWord8 the_gc_thread[sizeof(gc_thread) + 64 * sizeof(gen_workspace)]
-    ATTRIBUTE_ALIGNED(64);
+    ATTRIBUTE_ALIGNED(GEN_WORKSPACE_ALIGNMENT);
 #endif // THREADED_RTS
 
 /* Note [n_gc_threads]


=====================================
rts/sm/GCThread.h
=====================================
@@ -75,6 +75,14 @@
 
    ------------------------------------------------------------------------- */
 
+// align so that:
+//  * no two threads' workspaces fall in the same cache-line
+//  * computing gct->gens[n] is a shift, not a multiply
+//    fails if the size is <64, which is why we need the pad above
+// We use 128-bytes here as this is the cache-line size of new Apple ARMv8
+// platforms.
+#define GEN_WORKSPACE_ALIGNMENT CACHELINE_SIZE
+
 typedef struct gen_workspace_ {
     generation * gen;           // the gen for this workspace
     struct gc_thread_ * my_gct; // the gc_thread that contains this workspace
@@ -101,9 +109,7 @@ typedef struct gen_workspace_ {
     bdescr *     part_list;
     StgWord      n_part_blocks;      // count of above
     StgWord      n_part_words;
-} gen_workspace ATTRIBUTE_ALIGNED(64);
-// align so that computing gct->gens[n] is a shift, not a multiply
-// fails if the size is <64, which is why we need the pad above
+} gen_workspace ATTRIBUTE_ALIGNED(GEN_WORKSPACE_ALIGNMENT);
 
 /* ----------------------------------------------------------------------------
    GC thread object



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3da67f403eef8e3316e3bbcb4fe5639436312301

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3da67f403eef8e3316e3bbcb4fe5639436312301
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