Request that the one TB returns immediately, so that
we release the exclusive lock as soon as possible.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 accel/tcg/cpu-exec.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 2206c463f5..5bb099174f 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -330,8 +330,7 @@ void cpu_exec_step_atomic(CPUState *cpu)
     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
     TranslationBlock *tb;
     target_ulong cs_base, pc;
-    uint32_t flags;
-    uint32_t cflags = (curr_cflags(cpu) & ~CF_PARALLEL) | 1;
+    uint32_t flags, cflags;
     int tb_exit;
 
     if (sigsetjmp(cpu->jmp_env, 0) == 0) {
@@ -341,8 +340,14 @@ void cpu_exec_step_atomic(CPUState *cpu)
         cpu->running = true;
 
         cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
-        tb = tb_lookup(cpu, pc, cs_base, flags, cflags);
 
+        cflags = curr_cflags(cpu);
+        /* Execute in a serial context. */
+        cflags &= ~CF_PARALLEL;
+        /* After 1 insn, return and release the exclusive lock. */
+        cflags |= CF_NO_GOTO_TB | CF_NO_GOTO_PTR | 1;
+
+        tb = tb_lookup(cpu, pc, cs_base, flags, cflags);
         if (tb == NULL) {
             mmap_lock();
             tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
-- 
2.25.1

On Mon, 12 Jul 2021 at 16:46, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Request that the one TB returns immediately, so that
> we release the exclusive lock as soon as possible.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  accel/tcg/cpu-exec.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index 2206c463f5..5bb099174f 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -330,8 +330,7 @@ void cpu_exec_step_atomic(CPUState *cpu)
>      CPUArchState *env = (CPUArchState *)cpu->env_ptr;
>      TranslationBlock *tb;
>      target_ulong cs_base, pc;
> -    uint32_t flags;
> -    uint32_t cflags = (curr_cflags(cpu) & ~CF_PARALLEL) | 1;
> +    uint32_t flags, cflags;
>      int tb_exit;
>
>      if (sigsetjmp(cpu->jmp_env, 0) == 0) {
> @@ -341,8 +340,14 @@ void cpu_exec_step_atomic(CPUState *cpu)
>          cpu->running = true;
>
>          cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
> -        tb = tb_lookup(cpu, pc, cs_base, flags, cflags);
>
> +        cflags = curr_cflags(cpu);
> +        /* Execute in a serial context. */
> +        cflags &= ~CF_PARALLEL;
> +        /* After 1 insn, return and release the exclusive lock. */
> +        cflags |= CF_NO_GOTO_TB | CF_NO_GOTO_PTR | 1;
> +
> +        tb = tb_lookup(cpu, pc, cs_base, flags, cflags);
>          if (tb == NULL) {
>              mmap_lock();
>              tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);

So previously we would have executed possibly a chain of TBs
before releasing the lock, and now we definitely execute just one?
(I guess the execute-a-chain case is unlikely given the TB
only has one insn and we know it's an exclusive insn...)

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM

On 7/17/21 10:43 AM, Peter Maydell wrote:
> On Mon, 12 Jul 2021 at 16:46, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>
>> Request that the one TB returns immediately, so that
>> we release the exclusive lock as soon as possible.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   accel/tcg/cpu-exec.c | 11 ++++++++---
>>   1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
>> index 2206c463f5..5bb099174f 100644
>> --- a/accel/tcg/cpu-exec.c
>> +++ b/accel/tcg/cpu-exec.c
>> @@ -330,8 +330,7 @@ void cpu_exec_step_atomic(CPUState *cpu)
>>       CPUArchState *env = (CPUArchState *)cpu->env_ptr;
>>       TranslationBlock *tb;
>>       target_ulong cs_base, pc;
>> -    uint32_t flags;
>> -    uint32_t cflags = (curr_cflags(cpu) & ~CF_PARALLEL) | 1;
>> +    uint32_t flags, cflags;
>>       int tb_exit;
>>
>>       if (sigsetjmp(cpu->jmp_env, 0) == 0) {
>> @@ -341,8 +340,14 @@ void cpu_exec_step_atomic(CPUState *cpu)
>>           cpu->running = true;
>>
>>           cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
>> -        tb = tb_lookup(cpu, pc, cs_base, flags, cflags);
>>
>> +        cflags = curr_cflags(cpu);
>> +        /* Execute in a serial context. */
>> +        cflags &= ~CF_PARALLEL;
>> +        /* After 1 insn, return and release the exclusive lock. */
>> +        cflags |= CF_NO_GOTO_TB | CF_NO_GOTO_PTR | 1;
>> +
>> +        tb = tb_lookup(cpu, pc, cs_base, flags, cflags);
>>           if (tb == NULL) {
>>               mmap_lock();
>>               tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
> 
> So previously we would have executed possibly a chain of TBs
> before releasing the lock, and now we definitely execute just one?

Correct.

> (I guess the execute-a-chain case is unlikely given the TB
> only has one insn and we know it's an exclusive insn...)

I think it's actually likely.  While the tb would definitely end after one insn, we had 
passed nothing down that would lead to returning to the main loop.


r~

> 
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
> 
> thanks
> -- PMM
> 

Richard Henderson <richard.henderson@linaro.org> writes:

> Request that the one TB returns immediately, so that
> we release the exclusive lock as soon as possible.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

-- 
Alex Bennée