comment updates

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

diff --git a/rts/sm/GCThread.h b/rts/sm/GCThread.h
index 42d20bb..d4376f7 100644 (file)
--- a/rts/sm/GCThread.h
+++ b/rts/sm/GCThread.h
@@ -105,7 +105,7 @@ typedef struct step_workspace_ {
    GC thread object
 
    Every GC thread has one of these. It contains all the step specific
    GC thread object
 
    Every GC thread has one of these. It contains all the step specific

-   workspaces and other GC thread loacl information. At some later
+   workspaces and other GC thread local information. At some later

    point it maybe useful to move this other into the TLS store of the
    GC threads
    ------------------------------------------------------------------------- */
    point it maybe useful to move this other into the TLS store of the
    GC threads
    ------------------------------------------------------------------------- */

@@ -185,7 +185,13 @@ 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
 /* -----------------------------------------------------------------------------
    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

-   into a global register variable if possible.
+   into a global register variable if possible; if we don't have a
+   register then use gcc's __thread extension to create a thread-local
+   variable.
+
+   Even on x86 where registers are scarce, it is worthwhile using a
+   register variable here: I measured about a 2-5% slowdown with the
+   __thread version.

    -------------------------------------------------------------------------- */
 
 #define GLOBAL_REG_DECL(type,name,reg) register type name REG(reg);
    -------------------------------------------------------------------------- */
 
 #define GLOBAL_REG_DECL(type,name,reg) register type name REG(reg);