[Qemu-devel] [PATCH 2/8] cpu-exec: remove tb_lock from hot path

["Emilio G. Cota" <cota@braap.org>]

Signed-off-by: Emilio G. Cota <cota@braap.org>
---
 cpu-exec.c | 38 +++++++++++---------------------------
 1 file changed, 11 insertions(+), 27 deletions(-)

diff --git a/cpu-exec.c b/cpu-exec.c
index 041f8b7..63d739a 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -309,34 +309,18 @@ static TranslationBlock *tb_find_slow(CPUState *cpu,
     TranslationBlock *tb;
 
     tb = tb_find_physical(cpu, pc, cs_base, flags);
-    if (tb) {
-        goto found;
-    }
-
-#ifdef CONFIG_USER_ONLY
-    /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
-     * taken outside tb_lock.  Since we're momentarily dropping
-     * tb_lock, there's a chance that our desired tb has been
-     * translated.
-     */
-    tb_unlock();
-    mmap_lock();
-    tb_lock();
-    tb = tb_find_physical(cpu, pc, cs_base, flags);
-    if (tb) {
+    if (!tb) {
+        mmap_lock();
+        tb_lock();
+        tb = tb_find_physical(cpu, pc, cs_base, flags);
+        if (!tb) {
+            /* if no translated code available, then translate it now */
+            tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
+        }
+        tb_unlock();
         mmap_unlock();
-        goto found;
     }
-#endif
-
-    /* if no translated code available, then translate it now */
-    tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
-
-#ifdef CONFIG_USER_ONLY
-    mmap_unlock();
-#endif
 
-found:
     /* we add the TB in the virtual pc hash table */
     cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)] = tb;
     return tb;
@@ -355,7 +339,6 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
        always be the same before a given translated block
        is executed. */
     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
-    tb_lock();
     tb = cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)];
     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
                  tb->flags != flags)) {
@@ -379,9 +362,10 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
 #endif
     /* See if we can patch the calling TB. */
     if (*last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
+        tb_lock();
         tb_add_jump(*last_tb, tb_exit, tb);
+        tb_unlock();
     }
-    tb_unlock();
     return tb;
 }
 
-- 
2.5.0