[Qemu-devel] [RFC 7/7] [XXX] translate-all: generate TCG code without holding tb_lock

[Emilio G. Cota]

Generate new TBs without holding tb_lock, which should increase
scalability when running MTTCG for workloads that generate a lot
of code (e.g. booting linux).

XXX: Doesn't work :-) See the commit log from the previous patch.

Signed-off-by: Emilio G. Cota <address@hidden>
---
 accel/tcg/cpu-exec.c      |  8 +++++++-
 accel/tcg/translate-all.c | 18 ++++++++++++++++--
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 54ecae2..47f0882 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -351,6 +351,7 @@ static inline TranslationBlock *tb_find(CPUState *cpu,
              * single threaded the locks are NOPs.
              */
             mmap_lock();
+#ifdef CONFIG_USER_ONLY
             tb_lock();
             have_tb_lock = true;
 
@@ -362,7 +363,12 @@ static inline TranslationBlock *tb_find(CPUState *cpu,
                 /* if no translated code available, then translate it now */
                 tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
             }
-
+#else
+            /* tb_gen_code will acquire tb_lock.
+             * Just for the diff: note that have_tb_lock is local to tb_find! 
*/
+            have_tb_lock = true;
+            tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
+#endif
             mmap_unlock();
         }
 
diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index 125b1a8..da29bcc 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -878,8 +878,6 @@ static TranslationBlock *tb_alloc(target_ulong pc)
 {
     TranslationBlock *tb;
 
-    assert_tb_locked();
-
     tb = tcg_tb_alloc(&tcg_ctx);
     if (unlikely(tb == NULL)) {
         return NULL;
@@ -1314,7 +1312,9 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
 #ifdef CONFIG_PROFILER
     int64_t ti;
 #endif
+#ifdef CONFIG_USER_ONLY
     assert_memory_lock();
+#endif
 
     phys_pc = get_page_addr_code(env, pc);
     if (use_icount && !(cflags & CF_IGNORE_ICOUNT)) {
@@ -1429,6 +1429,20 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
     if ((pc & TARGET_PAGE_MASK) != virt_page2) {
         phys_page2 = get_page_addr_code(env, virt_page2);
     }
+    if (!have_tb_lock) {
+        TranslationBlock *t;
+
+        tb_lock();
+        /*
+         * There's a chance that our desired tb has been translated while
+         * we were translating it.
+         */
+        t = tb_htable_lookup(cpu, pc, cs_base, flags);
+        if (unlikely(t)) {
+            /* this is very unlikely so just waste the TB space we just used */
+            return t;
+        }
+    }
     /* As long as consistency of the TB stuff is provided by tb_lock in user
      * mode and is implicit in single-threaded softmmu emulation, no explicit
      * memory barrier is required before tb_link_page() makes the TB visible
-- 
2.7.4