From: Simon Marlow <marlowsd@gmail.com>
Date: Fri, 6 Mar 2009 10:00:18 +0000 (+0000)
Subject: Partial fix for #2917
X-Git-Tag: 2009-03-13~10
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=1b62aecee4a58f52999cfa53f1c6b7744b29b808;p=ghc-hetmet.git

Partial fix for #2917

 - add newAlignedPinnedByteArray# for allocating pinned BAs with
   arbitrary alignment

 - the old newPinnedByteArray# now aligns to 16 bytes

Foreign.alloca will use newAlignedPinnedByteArray#, and so might end
up wasting less space than before (we used to align to 8 by default).
Foreign.allocaBytes and Foreign.mallocForeignPtrBytes will get 16-byte
aligned memory, which is enough to avoid problems with SSE
instructions on x86, for example.

There was a bug in the old newPinnedByteArray#: it aligned to 8 bytes,
but would have failed if the header was not a multiple of 8
(fortunately it always was, even with profiling).  Also we
occasionally wasted some space unnecessarily due to alignment in
allocatePinned().

I haven't done anything about Foreign.malloc/mallocBytes, which will
give you the same alignment guarantees as malloc() (8 bytes on
Linux/x86 here).
---

diff --git a/compiler/prelude/primops.txt.pp b/compiler/prelude/primops.txt.pp
index 3779a79..942adb0 100644
--- a/compiler/prelude/primops.txt.pp
+++ b/compiler/prelude/primops.txt.pp
@@ -814,6 +814,11 @@ primop  NewPinnedByteArrayOp_Char "newPinnedByteArray#" GenPrimOp
    {Create a mutable byte array that the GC guarantees not to move.}
    with out_of_line = True
 
+primop  NewAlignedPinnedByteArrayOp_Char "newAlignedPinnedByteArray#" GenPrimOp
+   Int# -> Int# -> State# s -> (# State# s, MutableByteArray# s #)
+   {Create a mutable byte array, aligned by the specified amount, that the GC guarantees not to move.}
+   with out_of_line = True
+
 primop  ByteArrayContents_Char "byteArrayContents#" GenPrimOp
    ByteArray# -> Addr#
    {Intended for use with pinned arrays; otherwise very unsafe!}
diff --git a/includes/StgMiscClosures.h b/includes/StgMiscClosures.h
index 94244a9..e2ec9e4 100644
--- a/includes/StgMiscClosures.h
+++ b/includes/StgMiscClosures.h
@@ -540,6 +540,7 @@ RTS_FUN(word64ToIntegerzh_fast);
 RTS_FUN(unsafeThawArrayzh_fast);
 RTS_FUN(newByteArrayzh_fast);
 RTS_FUN(newPinnedByteArrayzh_fast);
+RTS_FUN(newAlignedPinnedByteArrayzh_fast);
 RTS_FUN(newArrayzh_fast);
 
 RTS_FUN(newMutVarzh_fast);
diff --git a/rts/Linker.c b/rts/Linker.c
index dc0d344..f701377 100644
--- a/rts/Linker.c
+++ b/rts/Linker.c
@@ -692,6 +692,7 @@ typedef struct _RtsSymbolVal {
       SymI_HasProto(noDuplicatezh_fast)			\
       SymI_HasProto(atomicModifyMutVarzh_fast)		\
       SymI_HasProto(newPinnedByteArrayzh_fast)		\
+      SymI_HasProto(newAlignedPinnedByteArrayzh_fast)	\
       SymI_HasProto(newSpark)				\
       SymI_HasProto(orIntegerzh_fast)			\
       SymI_HasProto(performGC)				\
diff --git a/rts/PrimOps.cmm b/rts/PrimOps.cmm
index a6e221b..272c705 100644
--- a/rts/PrimOps.cmm
+++ b/rts/PrimOps.cmm
@@ -83,6 +83,9 @@ newByteArrayzh_fast
     RET_P(p);
 }
 
+#define BA_ALIGN 16
+#define BA_MASK  (BA_ALIGN-1)
+
 newPinnedByteArrayzh_fast
 {
     W_ words, payload_words, n, p;
@@ -91,24 +94,45 @@ newPinnedByteArrayzh_fast
     n = R1;
     payload_words = ROUNDUP_BYTES_TO_WDS(n);
 
-    // We want an 8-byte aligned array.  allocatePinned() gives us
+    words = payload_words + ((SIZEOF_StgArrWords + BA_MASK) & ~BA_MASK);
+
+    ("ptr" p) = foreign "C" allocatePinned(words) [];
+    TICK_ALLOC_PRIM(SIZEOF_StgArrWords,WDS(payload_words),0);
+
+    // This bumps p forwards so that the payload falls on an R2-byte boundary.
+    p = p + ((-p - SIZEOF_StgArrWords) & BA_MASK);
+
+    SET_HDR(p, stg_ARR_WORDS_info, W_[CCCS]);
+    StgArrWords_words(p) = payload_words;
+    RET_P(p);
+}
+
+newAlignedPinnedByteArrayzh_fast
+{
+    W_ words, payload_words, n, p, mask;
+
+    MAYBE_GC(NO_PTRS,newAlignedPinnedByteArrayzh_fast);
+    n = R1;
+
+    if (R2 > SIZEOF_W) {
+        mask = R2 - 1;
+    } else {
+        mask = 0;
+    }
+
+    payload_words = ROUNDUP_BYTES_TO_WDS(n);
+
+    // We want an <align>-byte aligned array.  allocatePinned() gives us
     // 8-byte aligned memory by default, but we want to align the
     // *goods* inside the ArrWords object, so we have to check the
     // size of the ArrWords header and adjust our size accordingly.
-    words = BYTES_TO_WDS(SIZEOF_StgArrWords) + payload_words;
-    if ((SIZEOF_StgArrWords & 7) != 0) {
-	words = words + 1;
-    }
+    words = payload_words + ((SIZEOF_StgArrWords + mask) & ~mask);
 
     ("ptr" p) = foreign "C" allocatePinned(words) [];
     TICK_ALLOC_PRIM(SIZEOF_StgArrWords,WDS(payload_words),0);
 
-    // Again, if the ArrWords header isn't a multiple of 8 bytes, we
-    // have to push the object forward one word so that the goods
-    // fall on an 8-byte boundary.
-    if ((SIZEOF_StgArrWords & 7) != 0) {
-	p = p + WDS(1);
-    }
+    // This bumps p forwards so that the payload falls on an R2-byte boundary.
+    p = p + ((-p - SIZEOF_StgArrWords) & mask);
 
     SET_HDR(p, stg_ARR_WORDS_info, W_[CCCS]);
     StgArrWords_words(p) = payload_words;
diff --git a/rts/sm/Compact.c b/rts/sm/Compact.c
index 6758cfa..5f56c1e 100644
--- a/rts/sm/Compact.c
+++ b/rts/sm/Compact.c
@@ -490,6 +490,10 @@ update_fwd_large( bdescr *bd )
 
   for (; bd != NULL; bd = bd->link) {
 
+    // nothing to do in a pinned block; it might not even have an object
+    // at the beginning.
+    if (bd->flags & BF_PINNED) continue;
+
     p = bd->start;
     info  = get_itbl((StgClosure *)p);
 
diff --git a/rts/sm/Evac.c b/rts/sm/Evac.c
index 1c453fc..8d37f27 100644
--- a/rts/sm/Evac.c
+++ b/rts/sm/Evac.c
@@ -248,10 +248,6 @@ evacuate_large(StgPtr p)
   stp = bd->step;
   ACQUIRE_SPIN_LOCK(&stp->sync_large_objects);
 
-  // object must be at the beginning of the block (or be a ByteArray)
-  ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS ||
-	 (((W_)p & BLOCK_MASK) == 0));
-
   // already evacuated? 
   if (bd->flags & BF_EVACUATED) { 
     /* Don't forget to set the gct->failed_to_evac flag if we didn't get
@@ -287,11 +283,23 @@ evacuate_large(StgPtr p)
   }
 
   ws = &gct->steps[new_stp->abs_no];
+
   bd->flags |= BF_EVACUATED;
   bd->step = new_stp;
   bd->gen_no = new_stp->gen_no;
-  bd->link = ws->todo_large_objects;
-  ws->todo_large_objects = bd;
+
+  // If this is a block of pinned objects, we don't have to scan
+  // these objects, because they aren't allowed to contain any
+  // pointers.  For these blocks, we skip the scavenge stage and put
+  // them straight on the scavenged_large_objects list.
+  if (bd->flags & BF_PINNED) {
+      ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS);
+      dbl_link_onto(bd, &ws->step->scavenged_large_objects);
+      ws->step->n_scavenged_large_blocks += bd->blocks;
+  } else {
+      bd->link = ws->todo_large_objects;
+      ws->todo_large_objects = bd;
+  }
 
   RELEASE_SPIN_LOCK(&stp->sync_large_objects);
 }
diff --git a/rts/sm/Storage.c b/rts/sm/Storage.c
index 36741a6..9dea30e 100644
--- a/rts/sm/Storage.c
+++ b/rts/sm/Storage.c
@@ -808,7 +808,9 @@ allocatePinned( lnat n )
     // If the request is for a large object, then allocate()
     // will give us a pinned object anyway.
     if (n >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
-	return allocate(n);
+	p = allocate(n);
+        Bdescr(p)->flags |= BF_PINNED;
+        return p;
     }
 
     ACQUIRE_SM_LOCK;
@@ -816,13 +818,6 @@ allocatePinned( lnat n )
     TICK_ALLOC_HEAP_NOCTR(n);
     CCS_ALLOC(CCCS,n);
 
-    // we always return 8-byte aligned memory.  bd->free must be
-    // 8-byte aligned to begin with, so we just round up n to
-    // the nearest multiple of 8 bytes.
-    if (sizeof(StgWord) == 4) {
-	n = (n+1) & ~1;
-    }
-
     // If we don't have a block of pinned objects yet, or the current
     // one isn't large enough to hold the new object, allocate a new one.
     if (bd == NULL || (bd->free + n) > (bd->start + BLOCK_SIZE_W)) {