[Qemu-devel] [PATCH 08/10] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump()

[Paolo Bonzini <pbonzini@redhat.com>]

From: Sergey Fedorov <serge.fdrv@gmail.com>

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20160715175852.30749-11-sergey.fedorov@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 cpu-exec.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/cpu-exec.c b/cpu-exec.c
index 7ca2b71..bd9fa5a 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -282,7 +282,8 @@ static TranslationBlock *tb_find_physical(CPUState *cpu,
 static TranslationBlock *tb_find_slow(CPUState *cpu,
                                       target_ulong pc,
                                       target_ulong cs_base,
-                                      uint32_t flags)
+                                      uint32_t flags,
+                                      bool *have_tb_lock)
 {
     TranslationBlock *tb;
 
@@ -295,6 +296,7 @@ static TranslationBlock *tb_find_slow(CPUState *cpu,
          */
         mmap_lock();
         tb_lock();
+        *have_tb_lock = true;
 
         /* There's a chance that our desired tb has been translated while
          * taking the locks so we check again inside the lock.
@@ -305,7 +307,6 @@ static TranslationBlock *tb_find_slow(CPUState *cpu,
             tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
         }
 
-        tb_unlock();
         mmap_unlock();
     }
 
@@ -322,6 +323,7 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
     TranslationBlock *tb;
     target_ulong cs_base, pc;
     uint32_t flags;
+    bool have_tb_lock = false;
 
     /* we record a subset of the CPU state. It will
        always be the same before a given translated block
@@ -330,7 +332,7 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu,
     tb = atomic_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
                  tb->flags != flags)) {
-        tb = tb_find_slow(cpu, pc, cs_base, flags);
+        tb = tb_find_slow(cpu, pc, cs_base, flags, &have_tb_lock);
     }
 #ifndef CONFIG_USER_ONLY
     /* We don't take care of direct jumps when address mapping changes in
@@ -343,13 +345,18 @@ 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();
+        if (!have_tb_lock) {
+            tb_lock();
+            have_tb_lock = true;
+        }
         /* Check if translation buffer has been flushed */
         if (cpu->tb_flushed) {
             cpu->tb_flushed = false;
         } else if (!tb->invalid) {
             tb_add_jump(last_tb, tb_exit, tb);
         }
+    }
+    if (have_tb_lock) {
         tb_unlock();
     }
     return tb;
-- 
2.7.4