From: Alex Bennée <alex.ben...@linaro.org>
Lock contention in the hot path of moving between existing patched
TranslationBlocks is the main drag in multithreaded performance. This
patch pushes the tb_lock() usage down to the two places that really need
it:
- code generation (tb_gen_code)
- jump patching (tb_add_jump)
The rest of the code doesn't really need to hold a lock as it is either
using per-CPU structures, atomically updated or designed to be used in
concurrent read situations (qht_lookup).
To keep things simple I removed the #ifdef CONFIG_USER_ONLY stuff as the
locks become NOPs anyway until the MTTCG work is completed.
Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
Reviewed-by: Richard Henderson <r...@twiddle.net>
Reviewed-by: Sergey Fedorov <sergey.fedo...@linaro.org>
Signed-off-by: Sergey Fedorov <sergey.fedo...@linaro.org>
---
v2 (hot path)
- Add r-b tags
v1 (hot path, split from base-patches series)
- revert name tweaking
- drop test jmp_list_next outside lock
- mention lock NOPs in comments
v3 (base-patches)
- fix merge conflicts with Sergey's patch
---
cpu-exec.c | 48 +++++++++++++++++++++---------------------------
1 file changed, 21 insertions(+), 27 deletions(-)
diff --git a/cpu-exec.c b/cpu-exec.c
index 07dc50c56e8d..4eabd534aba0 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -286,35 +286,29 @@ static TranslationBlock *tb_find_slow(CPUState *cpu,
TranslationBlock *tb;
tb = tb_find_physical(cpu, pc, cs_base, flags);
- if (tb) {
- goto found;
- }
+ if (!tb) {
-#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) {
- mmap_unlock();
- goto found;
- }
-#endif
+ /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
+ * taken outside tb_lock. As system emulation is currently
+ * single threaded the locks are NOPs.
+ */
+ mmap_lock();
+ tb_lock();
- /* if no translated code available, then translate it now */
- tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
+ /* There's a chance that our desired tb has been translated while
+ * taking the locks so we check again inside the 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);
+ }
-#ifdef CONFIG_USER_ONLY
- mmap_unlock();
-#endif
+ tb_unlock();
+ mmap_unlock();
+ }
-found:
- /* we add the TB in the virtual pc hash table */
+ /* We add the TB in the virtual pc hash table for the fast lookup */
atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
return tb;
}
@@ -332,7 +326,6 @@ 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 = 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)) {
@@ -349,14 +342,15 @@ 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();
/* Check if translation buffer has been flushed */
if (cpu->tb_flushed) {
cpu->tb_flushed = false;
} else if (!tb_is_invalid(tb)) {
tb_add_jump(last_tb, tb_exit, tb);
}
+ tb_unlock();
}
- tb_unlock();
return tb;
}
--
1.9.1
