From d381592a92ad816343ce61a6f5511b89041ff299 Mon Sep 17 00:00:00 2001 From: Pierrick Bouvier Date: Sun, 24 Nov 2024 15:14:59 -0800 Subject: [PATCH] plugins: optimize cpu_index code generation When running with a single vcpu, we can return a constant instead of a load when accessing cpu_index. A side effect is that all tcg operations using it are optimized, most notably scoreboard access. When running a simple loop in user-mode, the speedup is around 20%. Signed-off-by: Pierrick Bouvier --- v2: - no need to do a flush, as user-mode already does it when spawning a second cpu (to honor CF_PARALLEL flags). - change condition detection to use CF_PARALLEL instead Signed-off-by: Pierrick Bouvier --- accel/tcg/plugin-gen.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/accel/tcg/plugin-gen.c b/accel/tcg/plugin-gen.c index 0f47bfbb4899d..961d9305913a8 100644 --- a/accel/tcg/plugin-gen.c +++ b/accel/tcg/plugin-gen.c @@ -102,6 +102,15 @@ static void gen_disable_mem_helper(void) static TCGv_i32 gen_cpu_index(void) { + /* + * Optimize when we run with a single vcpu. All values using cpu_index, + * including scoreboard index, will be optimized out. + * User-mode calls tb_flush when setting this flag. In system-mode, all + * vcpus are created before generating code. + */ + if (!tcg_cflags_has(current_cpu, CF_PARALLEL)) { + return tcg_constant_i32(current_cpu->cpu_index); + } TCGv_i32 cpu_index = tcg_temp_ebb_new_i32(); tcg_gen_ld_i32(cpu_index, tcg_env, -offsetof(ArchCPU, env) + offsetof(CPUState, cpu_index));