From 518615c6503ad78d3bb67ddf1cd848c4a41de02e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Alex=20Benn=C3=A9e?= Date: Fri, 15 Jul 2016 20:58:49 +0300 Subject: [PATCH] tcg: cpu-exec: remove tb_lock from the hot-path MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Richard Henderson Reviewed-by: Sergey Fedorov Signed-off-by: Sergey Fedorov Message-Id: <20160715175852.30749-10-sergey.fedorov@linaro.org> Signed-off-by: Paolo Bonzini --- cpu-exec.c | 48 +++++++++++++++++++++--------------------------- 1 file changed, 21 insertions(+), 27 deletions(-) diff --git a/cpu-exec.c b/cpu-exec.c index cdaab1dbcd..7ca2b71a89 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -287,35 +287,29 @@ 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_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(); + + /* 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); + } + + 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 */ + /* 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; } @@ -333,7 +327,6 @@ 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_rcu_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)) { @@ -350,14 +343,15 @@ 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->invalid) { tb_add_jump(last_tb, tb_exit, tb); } + tb_unlock(); } - tb_unlock(); return tb; }