SPARC NCG: Add a comment explaining why we can't used a pinned reg for gct

[ghc-hetmet.git] / rts / sm / GCThread.h

diff --git a/rts/sm/GCThread.h b/rts/sm/GCThread.h
index 3ee2757..f91092b 100644 (file)
--- a/rts/sm/GCThread.h
+++ b/rts/sm/GCThread.h
@@ -15,6 +15,7 @@
 #define GCTHREAD_H
 
 #include "OSThreads.h"
+#include "WSDeque.h"
 
 /* -----------------------------------------------------------------------------
    General scheme
@@ -74,20 +75,21 @@
 
 typedef struct step_workspace_ {
     step * step;               // the step for this workspace 
-    struct gc_thread_ * gct;    // the gc_thread that contains this workspace
+    struct gc_thread_ * my_gct; // the gc_thread that contains this workspace
 
     // where objects to be scavenged go
     bdescr *     todo_bd;
     StgPtr       todo_free;            // free ptr for todo_bd
     StgPtr       todo_lim;             // lim for todo_bd
 
-    bdescr *     buffer_todo_bd;     // buffer to reduce contention
-                                     // on the step's todos list
+    WSDeque *    todo_q;
+    bdescr *     todo_overflow;
+    nat          n_todo_overflow;
 
     // where large objects to be scavenged go
     bdescr *     todo_large_objects;
 
-    // Objects that have already been, scavenged.
+    // Objects that have already been scavenged.
     bdescr *     scavd_list;
     nat          n_scavd_blocks;     // count of blocks in this list
 
@@ -95,7 +97,7 @@ typedef struct step_workspace_ {
     bdescr *     part_list;
     unsigned int n_part_blocks;      // count of above
 
-    StgWord pad[5];
+    StgWord pad[3];
 
 } step_workspace ATTRIBUTE_ALIGNED(64);
 // align so that computing gct->steps[n] is a shift, not a multiply
@@ -187,8 +189,6 @@ typedef struct gc_thread_ {
 
 extern nat n_gc_threads;
 
-extern gc_thread **gc_threads;
-
 /* -----------------------------------------------------------------------------
    The gct variable is thread-local and points to the current thread's
    gc_thread structure.  It is heavily accessed, so we try to put gct
@@ -201,15 +201,41 @@ extern gc_thread **gc_threads;
    __thread version.
    -------------------------------------------------------------------------- */
 
+extern gc_thread **gc_threads;
+
+#if defined(THREADED_RTS)
+
 #define GLOBAL_REG_DECL(type,name,reg) register type name REG(reg);
 
-#if defined(sparc_HOST_ARCH)
-// Don't use REG_base or R1 for gct on SPARC because they're getting clobbered 
-//     by something else. Not sure what yet. -- BL 2009/01/03
+#define SET_GCT(to) gct = (to)
+
+
+
+#if (defined(i386_HOST_ARCH) && defined(linux_HOST_OS))
+// Using __thread is better than stealing a register on x86/Linux, because
+// we have too few registers available.  In my tests it was worth
+// about 5% in GC performance, but of course that might change as gcc
+// improves. -- SDM 2009/04/03
 
 extern __thread gc_thread* gct;
 #define DECLARE_GCT __thread gc_thread* gct;
 
+
+#elif defined(sparc_TARGET_ARCH)
+// On SPARC we can't pin gct to a register. Names like %l1 are just offsets
+//     into the register window, which change on each function call.
+//     
+//     There are eight global (non-window) registers, but they're used for other purposes.
+//     %g0     -- always zero
+//     %g1     -- volatile over function calls, used by the linker
+//     %g2-%g3 -- used as scratch regs by the C compiler (caller saves)
+//     %g4     -- volatile over function calls, used by the linker
+//     %g5-%g7 -- reserved by the OS
+
+extern __thread gc_thread* gct;
+#define DECLARE_GCT __thread gc_thread* gct;
+
+
 #elif defined(REG_Base) && !defined(i386_HOST_ARCH)
 // on i386, REG_Base is %ebx which is also used for PIC, so we don't
 // want to steal it
@@ -217,11 +243,13 @@ extern __thread gc_thread* gct;
 GLOBAL_REG_DECL(gc_thread*, gct, REG_Base)
 #define DECLARE_GCT /* nothing */
 
+
 #elif defined(REG_R1)
 
 GLOBAL_REG_DECL(gc_thread*, gct, REG_R1)
 #define DECLARE_GCT /* nothing */
 
+
 #elif defined(__GNUC__)
 
 extern __thread gc_thread* gct;
@@ -233,5 +261,15 @@ extern __thread gc_thread* gct;
 
 #endif
 
+#else  // not the threaded RTS
+
+extern StgWord8 the_gc_thread[];
+
+#define gct ((gc_thread*)&the_gc_thread)
+#define SET_GCT(to) /*nothing*/
+#define DECLARE_GCT /*nothing*/
+
+#endif
+
 #endif // GCTHREAD_H