Re: [Qemu-devel] [RFC v2 11/11] tcg: Make tb_flush() thread safe
Sergey Fedorov writes:
> On 14/07/16 11:41, Alex Bennée wrote:
>> Sergey Fedorov writes:
>>
>>> From: Sergey Fedorov
>>>
>>> Use async_safe_run_on_cpu() to make tb_flush() thread safe.
>>>
>>> Signed-off-by: Sergey Fedorov
>>> Signed-off-by: Sergey Fedorov
>>> ---
>>>
>>> Changes in v2:
>>> - stale comment about unsafe tb_flush() removed
>>> ---
>>> translate-all.c | 13 -
>>> 1 file changed, 8 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/translate-all.c b/translate-all.c
>>> index eaa95e4cd7dc..e69b5d4e889e 100644
>>> --- a/translate-all.c
>>> +++ b/translate-all.c
>>> @@ -831,8 +831,7 @@ static void page_flush_tb(void)
>>> }
>>>
>>> /* flush all the translation blocks */
>>> -/* XXX: tb_flush is currently not thread safe */
>>> -void tb_flush(CPUState *cpu)
>>> +static void do_tb_flush(CPUState *cpu, void *data)
>>> {
>>> #if defined(DEBUG_FLUSH)
>>> printf("qemu: flush code_size=%ld nb_tbs=%d avg_tb_size=%ld\n",
>>> @@ -861,6 +860,11 @@ void tb_flush(CPUState *cpu)
>>> tcg_ctx.tb_ctx.tb_flush_count++;
>>> }
>>>
>>> +void tb_flush(CPUState *cpu)
>>> +{
>>> +async_safe_run_on_cpu(cpu, do_tb_flush, NULL);
>>> +}
>>> +
>>> #ifdef DEBUG_TB_CHECK
>>>
>>> static void
>>> @@ -1163,9 +1167,8 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>>> buffer_overflow:
>>> /* flush must be done */
>>> tb_flush(cpu);
>>> -/* cannot fail at this point */
>>> -tb = tb_alloc(pc);
>>> -assert(tb != NULL);
>>> +mmap_unlock();
>>> +cpu_loop_exit(cpu);
>> Given our other discussions about lock resetting I wonder if this is
>> another case where mmap_reset() could be called on cpu_loop_exit?
>
> As I can see, this is the only place mmap_unlock() have to be called
> right before cpu_loop_exit(). As I remember, all the other cased in
> user-mode emulation were restructured by Peter M. in his syscall/signal
> handling series. However, I like the idea to ensure that 'mmap_lock' is
> released on any cpu_loop_exit(). What do maintainers think?
>
> Kind regards,
> Sergey
>
>>
>>> }
>>>
>>> gen_code_buf = tcg_ctx.code_gen_ptr;
>> Otherwise so far the testing is looking pretty positive in linux-user:
>>
>> Tested-by: Alex Bennée
>> Reviewed-by: Alex Bennée
I should add for the testing to fail without this series I had to apply
the hot-path fixes otherwise lock contention has a serialising affect on
the flushes anyway.
>>
>>
>> --
>> Alex Bennée
--
Alex Bennée
Re: [Qemu-devel] [RFC v2 11/11] tcg: Make tb_flush() thread safe
On 14/07/16 11:41, Alex Bennée wrote:
> Sergey Fedorov writes:
>
>> From: Sergey Fedorov
>>
>> Use async_safe_run_on_cpu() to make tb_flush() thread safe.
>>
>> Signed-off-by: Sergey Fedorov
>> Signed-off-by: Sergey Fedorov
>> ---
>>
>> Changes in v2:
>> - stale comment about unsafe tb_flush() removed
>> ---
>> translate-all.c | 13 -
>> 1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/translate-all.c b/translate-all.c
>> index eaa95e4cd7dc..e69b5d4e889e 100644
>> --- a/translate-all.c
>> +++ b/translate-all.c
>> @@ -831,8 +831,7 @@ static void page_flush_tb(void)
>> }
>>
>> /* flush all the translation blocks */
>> -/* XXX: tb_flush is currently not thread safe */
>> -void tb_flush(CPUState *cpu)
>> +static void do_tb_flush(CPUState *cpu, void *data)
>> {
>> #if defined(DEBUG_FLUSH)
>> printf("qemu: flush code_size=%ld nb_tbs=%d avg_tb_size=%ld\n",
>> @@ -861,6 +860,11 @@ void tb_flush(CPUState *cpu)
>> tcg_ctx.tb_ctx.tb_flush_count++;
>> }
>>
>> +void tb_flush(CPUState *cpu)
>> +{
>> +async_safe_run_on_cpu(cpu, do_tb_flush, NULL);
>> +}
>> +
>> #ifdef DEBUG_TB_CHECK
>>
>> static void
>> @@ -1163,9 +1167,8 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>> buffer_overflow:
>> /* flush must be done */
>> tb_flush(cpu);
>> -/* cannot fail at this point */
>> -tb = tb_alloc(pc);
>> -assert(tb != NULL);
>> +mmap_unlock();
>> +cpu_loop_exit(cpu);
> Given our other discussions about lock resetting I wonder if this is
> another case where mmap_reset() could be called on cpu_loop_exit?
As I can see, this is the only place mmap_unlock() have to be called
right before cpu_loop_exit(). As I remember, all the other cased in
user-mode emulation were restructured by Peter M. in his syscall/signal
handling series. However, I like the idea to ensure that 'mmap_lock' is
released on any cpu_loop_exit(). What do maintainers think?
Kind regards,
Sergey
>
>> }
>>
>> gen_code_buf = tcg_ctx.code_gen_ptr;
> Otherwise so far the testing is looking pretty positive in linux-user:
>
> Tested-by: Alex Bennée
> Reviewed-by: Alex Bennée
>
>
> --
> Alex Bennée
Re: [Qemu-devel] [RFC v2 11/11] tcg: Make tb_flush() thread safe
Sergey Fedorov writes:
> From: Sergey Fedorov
>
> Use async_safe_run_on_cpu() to make tb_flush() thread safe.
>
> Signed-off-by: Sergey Fedorov
> Signed-off-by: Sergey Fedorov
> ---
>
> Changes in v2:
> - stale comment about unsafe tb_flush() removed
> ---
> translate-all.c | 13 -
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/translate-all.c b/translate-all.c
> index eaa95e4cd7dc..e69b5d4e889e 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -831,8 +831,7 @@ static void page_flush_tb(void)
> }
>
> /* flush all the translation blocks */
> -/* XXX: tb_flush is currently not thread safe */
> -void tb_flush(CPUState *cpu)
> +static void do_tb_flush(CPUState *cpu, void *data)
> {
> #if defined(DEBUG_FLUSH)
> printf("qemu: flush code_size=%ld nb_tbs=%d avg_tb_size=%ld\n",
> @@ -861,6 +860,11 @@ void tb_flush(CPUState *cpu)
> tcg_ctx.tb_ctx.tb_flush_count++;
> }
>
> +void tb_flush(CPUState *cpu)
> +{
> +async_safe_run_on_cpu(cpu, do_tb_flush, NULL);
> +}
> +
> #ifdef DEBUG_TB_CHECK
>
> static void
> @@ -1163,9 +1167,8 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
> buffer_overflow:
> /* flush must be done */
> tb_flush(cpu);
> -/* cannot fail at this point */
> -tb = tb_alloc(pc);
> -assert(tb != NULL);
> +mmap_unlock();
> +cpu_loop_exit(cpu);
Given our other discussions about lock resetting I wonder if this is
another case where mmap_reset() could be called on cpu_loop_exit?
> }
>
> gen_code_buf = tcg_ctx.code_gen_ptr;
Otherwise so far the testing is looking pretty positive in linux-user:
Tested-by: Alex Bennée
Reviewed-by: Alex Bennée
--
Alex Bennée
Re: [Qemu-devel] [RFC v2 11/11] tcg: Make tb_flush() thread safe
On 07/07/16 00:15, Sergey Fedorov wrote: > From: Sergey Fedorov > > Use async_safe_run_on_cpu() to make tb_flush() thread safe. I've just realized that this allows to remove CPUState::tb_flushed as well. Regards, Sergey
