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-rw-r--r--ghc/rts/GC.c226
1 files changed, 108 insertions, 118 deletions
diff --git a/ghc/rts/GC.c b/ghc/rts/GC.c
index 0399d6034e..bc8546a115 100644
--- a/ghc/rts/GC.c
+++ b/ghc/rts/GC.c
@@ -4250,74 +4250,6 @@ gcCAFs(void)
/* -----------------------------------------------------------------------------
- Lazy black holing.
-
- Whenever a thread returns to the scheduler after possibly doing
- some work, we have to run down the stack and black-hole all the
- closures referred to by update frames.
- -------------------------------------------------------------------------- */
-
-static void
-threadLazyBlackHole(StgTSO *tso)
-{
- StgClosure *frame;
- StgRetInfoTable *info;
- StgClosure *bh;
- StgPtr stack_end;
-
- stack_end = &tso->stack[tso->stack_size];
-
- frame = (StgClosure *)tso->sp;
-
- while (1) {
- info = get_ret_itbl(frame);
-
- switch (info->i.type) {
-
- case UPDATE_FRAME:
- bh = ((StgUpdateFrame *)frame)->updatee;
-
- /* if the thunk is already blackholed, it means we've also
- * already blackholed the rest of the thunks on this stack,
- * so we can stop early.
- *
- * The blackhole made for a CAF is a CAF_BLACKHOLE, so they
- * don't interfere with this optimisation.
- */
- if (bh->header.info == &stg_BLACKHOLE_info) {
- return;
- }
-
- if (bh->header.info != &stg_CAF_BLACKHOLE_info) {
-#if (!defined(LAZY_BLACKHOLING)) && defined(DEBUG)
- debugBelch("Unexpected lazy BHing required at 0x%04lx\n",(long)bh);
-#endif
-#ifdef PROFILING
- // @LDV profiling
- // We pretend that bh is now dead.
- LDV_recordDead_FILL_SLOP_DYNAMIC((StgClosure *)bh);
-#endif
- SET_INFO(bh,&stg_BLACKHOLE_info);
-
- // We pretend that bh has just been created.
- LDV_RECORD_CREATE(bh);
- }
-
- frame = (StgClosure *) ((StgUpdateFrame *)frame + 1);
- break;
-
- case STOP_FRAME:
- return;
-
- // normal stack frames; do nothing except advance the pointer
- default:
- frame = (StgClosure *)((StgPtr)frame + stack_frame_sizeW(frame));
- }
- }
-}
-
-
-/* -----------------------------------------------------------------------------
* Stack squeezing
*
* Code largely pinched from old RTS, then hacked to bits. We also do
@@ -4328,12 +4260,11 @@ threadLazyBlackHole(StgTSO *tso)
struct stack_gap { StgWord gap_size; struct stack_gap *next_gap; };
static void
-threadSqueezeStack(StgTSO *tso)
+stackSqueeze(StgTSO *tso, StgPtr bottom)
{
StgPtr frame;
rtsBool prev_was_update_frame;
StgClosure *updatee = NULL;
- StgPtr bottom;
StgRetInfoTable *info;
StgWord current_gap_size;
struct stack_gap *gap;
@@ -4344,8 +4275,6 @@ threadSqueezeStack(StgTSO *tso)
// contains two values: the size of the gap, and the distance
// to the next gap (or the stack top).
- bottom = &(tso->stack[tso->stack_size]);
-
frame = tso->sp;
ASSERT(frame < bottom);
@@ -4363,20 +4292,6 @@ threadSqueezeStack(StgTSO *tso)
{
StgUpdateFrame *upd = (StgUpdateFrame *)frame;
- if (upd->updatee->header.info == &stg_BLACKHOLE_info) {
-
- // found a BLACKHOLE'd update frame; we've been here
- // before, in a previous GC, so just break out.
-
- // Mark the end of the gap, if we're in one.
- if (current_gap_size != 0) {
- gap = (struct stack_gap *)(frame-sizeofW(StgUpdateFrame));
- }
-
- frame += sizeofW(StgUpdateFrame);
- goto done_traversing;
- }
-
if (prev_was_update_frame) {
TICK_UPD_SQUEEZED();
@@ -4409,31 +4324,6 @@ threadSqueezeStack(StgTSO *tso)
// single update frame, or the topmost update frame in a series
else {
- StgClosure *bh = upd->updatee;
-
- // Do lazy black-holing
- if (bh->header.info != &stg_BLACKHOLE_info &&
- bh->header.info != &stg_CAF_BLACKHOLE_info) {
-#if (!defined(LAZY_BLACKHOLING)) && defined(DEBUG)
- debugBelch("Unexpected lazy BHing required at 0x%04lx",(long)bh);
-#endif
-#ifdef DEBUG
- // zero out the slop so that the sanity checker can tell
- // where the next closure is.
- DEBUG_FILL_SLOP(bh);
-#endif
-#ifdef PROFILING
- // We pretend that bh is now dead.
- // ToDo: is the slop filling the same as DEBUG_FILL_SLOP?
- LDV_recordDead_FILL_SLOP_DYNAMIC((StgClosure *)bh);
-#endif
- // Todo: maybe use SET_HDR() and remove LDV_RECORD_CREATE()?
- SET_INFO(bh,&stg_BLACKHOLE_info);
-
- // We pretend that bh has just been created.
- LDV_RECORD_CREATE(bh);
- }
-
prev_was_update_frame = rtsTrue;
updatee = upd->updatee;
frame += sizeofW(StgUpdateFrame);
@@ -4456,8 +4346,10 @@ threadSqueezeStack(StgTSO *tso)
}
}
-done_traversing:
-
+ if (current_gap_size != 0) {
+ gap = (struct stack_gap *) (frame - sizeofW(StgUpdateFrame));
+ }
+
// Now we have a stack with gaps in it, and we have to walk down
// shoving the stack up to fill in the gaps. A diagram might
// help:
@@ -4515,12 +4407,110 @@ done_traversing:
* turned on.
* -------------------------------------------------------------------------- */
void
-threadPaused(StgTSO *tso)
+threadPaused(Capability *cap, StgTSO *tso)
{
- if ( RtsFlags.GcFlags.squeezeUpdFrames == rtsTrue )
- threadSqueezeStack(tso); // does black holing too
- else
- threadLazyBlackHole(tso);
+ StgClosure *frame;
+ StgRetInfoTable *info;
+ StgClosure *bh;
+ StgPtr stack_end;
+ nat words_to_squeeze = 0;
+ nat weight = 0;
+ nat weight_pending = 0;
+ rtsBool prev_was_update_frame;
+
+ stack_end = &tso->stack[tso->stack_size];
+
+ frame = (StgClosure *)tso->sp;
+
+ while (1) {
+ // If we've already marked this frame, then stop here.
+ if (frame->header.info == (StgInfoTable *)&stg_marked_upd_frame_info) {
+ goto end;
+ }
+
+ info = get_ret_itbl(frame);
+
+ switch (info->i.type) {
+
+ case UPDATE_FRAME:
+
+ SET_INFO(frame, (StgInfoTable *)&stg_marked_upd_frame_info);
+
+ bh = ((StgUpdateFrame *)frame)->updatee;
+
+ if (closure_IND(bh) || bh->header.info == &stg_BLACKHOLE_info) {
+ IF_DEBUG(squeeze, debugBelch("suspending duplicate work: %d words of stack\n", (StgPtr)frame - tso->sp));
+
+ // If this closure is already an indirection, then
+ // suspend the computation up to this point:
+ suspendComputation(cap,tso,(StgPtr)frame);
+
+ // Now drop the update frame, and arrange to return
+ // the value to the frame underneath:
+ tso->sp = (StgPtr)frame + sizeofW(StgUpdateFrame) - 2;
+ tso->sp[1] = (StgWord)bh;
+ tso->sp[0] = (W_)&stg_enter_info;
+
+ // And continue with threadPaused; there might be
+ // yet more computation to suspend.
+ threadPaused(cap,tso);
+ return;
+ }
+
+ if (bh->header.info != &stg_CAF_BLACKHOLE_info) {
+#if (!defined(LAZY_BLACKHOLING)) && defined(DEBUG)
+ debugBelch("Unexpected lazy BHing required at 0x%04lx\n",(long)bh);
+#endif
+ // zero out the slop so that the sanity checker can tell
+ // where the next closure is.
+ DEBUG_FILL_SLOP(bh);
+#ifdef PROFILING
+ // @LDV profiling
+ // We pretend that bh is now dead.
+ LDV_recordDead_FILL_SLOP_DYNAMIC((StgClosure *)bh);
+#endif
+ SET_INFO(bh,&stg_BLACKHOLE_info);
+
+ // We pretend that bh has just been created.
+ LDV_RECORD_CREATE(bh);
+ }
+
+ frame = (StgClosure *) ((StgUpdateFrame *)frame + 1);
+ if (prev_was_update_frame) {
+ words_to_squeeze += sizeofW(StgUpdateFrame);
+ weight += weight_pending;
+ weight_pending = 0;
+ }
+ prev_was_update_frame = rtsTrue;
+ break;
+
+ case STOP_FRAME:
+ goto end;
+
+ // normal stack frames; do nothing except advance the pointer
+ default:
+ {
+ nat frame_size = stack_frame_sizeW(frame);
+ weight_pending += frame_size;
+ frame = (StgClosure *)((StgPtr)frame + frame_size);
+ prev_was_update_frame = rtsFalse;
+ }
+ }
+ }
+
+end:
+ IF_DEBUG(squeeze,
+ debugBelch("words_to_squeeze: %d, weight: %d, squeeze: %s\n",
+ words_to_squeeze, weight,
+ weight < words_to_squeeze ? "YES" : "NO"));
+
+ // Should we squeeze or not? Arbitrary heuristic: we squeeze if
+ // the number of words we have to shift down is less than the
+ // number of stack words we squeeze away by doing so.
+ if (1 /*RtsFlags.GcFlags.squeezeUpdFrames == rtsTrue &&
+ weight < words_to_squeeze*/) {
+ stackSqueeze(tso, (StgPtr)frame);
+ }
}
/* -----------------------------------------------------------------------------
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