https://git.ruby-lang.org/ruby.git/commit/?id=99b9145380

From 99b91453809be68c604f94416030addfff3d6142 Mon Sep 17 00:00:00 2001
From: Koichi Sasada <ko1@a...>
Date: Thu, 17 Dec 2020 04:06:04 +0900
Subject: relax synchronization on WB

Current synchronization is too much on write barriers.

diff --git a/gc.c b/gc.c
index a06f3ce..c067ac4 100644
--- a/gc.c
+++ b/gc.c
@@ -7689,7 +7689,11 @@ gc_writebarrier_generational(VALUE a, VALUE b, rb_objspace_t *objspace) https://github.com/ruby/ruby/blob/trunk/gc.c#L7689
 #if 1
     /* mark `a' and remember (default behavior) */
     if (!rgengc_remembered(objspace, a)) {
-	rgengc_remember(objspace, a);
+        RB_VM_LOCK_ENTER_NO_BARRIER();
+        {
+            rgengc_remember(objspace, a);
+        }
+        RB_VM_LOCK_LEAVE_NO_BARRIER();
 	gc_report(1, objspace, "gc_writebarrier_generational: %s (remembered) -> %s\n", obj_info(a), obj_info(b));
     }
 #else
@@ -7763,49 +7767,26 @@ void https://github.com/ruby/ruby/blob/trunk/gc.c#L7767
 rb_gc_writebarrier(VALUE a, VALUE b)
 {
     rb_objspace_t *objspace = &rb_objspace;
-    bool retry;
 
     if (RGENGC_CHECK_MODE && SPECIAL_CONST_P(a)) rb_bug("rb_gc_writebarrier: a is special const");
     if (RGENGC_CHECK_MODE && SPECIAL_CONST_P(b)) rb_bug("rb_gc_writebarrier: b is special const");
 
-  retry_:
-    retry = false;
     if (!is_incremental_marking(objspace)) {
         if (!RVALUE_OLD_P(a) || RVALUE_OLD_P(b)) {
             // do nothing
         }
         else {
-            RB_VM_LOCK_ENTER_NO_BARRIER(); // can change GC state
-            {
-                if (!is_incremental_marking(objspace)) {
-                    if (!RVALUE_OLD_P(a) || RVALUE_OLD_P(b)) {
-                        // do nothing
-                    }
-                    else {
-                        gc_writebarrier_generational(a, b, objspace);
-                    }
-                }
-                else {
-                    retry = true;
-                }
-            }
-            RB_VM_LOCK_LEAVE_NO_BARRIER();
+            gc_writebarrier_generational(a, b, objspace);
         }
     }
-    else { /* slow path */
-        RB_VM_LOCK_ENTER_NO_BARRIER(); // can change GC state
+    else {
+        /* slow path */
+        RB_VM_LOCK_ENTER_NO_BARRIER();
         {
-            if (is_incremental_marking(objspace)) {
-                gc_writebarrier_incremental(a, b, objspace);
-            }
-            else {
-                retry = true;
-            }
+            gc_writebarrier_incremental(a, b, objspace);
         }
         RB_VM_LOCK_LEAVE_NO_BARRIER();
     }
-    if (retry) goto retry_;
-
     return;
 }
 
-- 
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