[Mesa-dev] [PATCH 1/1] i965: Do not overwrite optimizer dumps

[Matt Turner]

On Wed, Nov 25, 2015 at 11:05 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> On Wed, Nov 25, 2015 at 10:52 AM, Matt Turner <mattst88 at gmail.com> wrote:
>> On Wed, Nov 25, 2015 at 10:46 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>>> On Wed, Nov 25, 2015 at 10:45 AM, Matt Turner <mattst88 at gmail.com> wrote:
>>>> On Wed, Nov 25, 2015 at 10:37 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>>>>> On Wed, Nov 25, 2015 at 10:31 AM, Matt Turner <mattst88 at gmail.com> wrote:
>>>>>> On Wed, Nov 25, 2015 at 4:15 AM, Juan A. Suarez Romero
>>>>>> <jasuarez at igalia.com> wrote:
>>>>>>> When using INTEL_DEBUG=optimizer, each optimizing step is dump to disk,
>>>>>>> in a separate file.
>>>>>>>
>>>>>>> But as fs_visitor::optimize() and vec4_visitor::run() are called more
>>>>>>> than once, it ends up overwriting the files already on disk, loosing
>>>>>>> then previous optimizer steps.
>>>>>>
>>>>>> Huh. I guess this happens when non-orthogonal state changes and we
>>>>>> recompile the program?
>>>>>>
>>>>>> If so, yeah, that would lead to some confusing results.
>>>>>>
>>>>>>> To avoid this, add a new static variable that tracks the global
>>>>>>> iteration across the entire life of the program running.
>>>>>>> ---
>>>>>>>  src/mesa/drivers/dri/i965/brw_fs.cpp   | 13 +++++++++----
>>>>>>>  src/mesa/drivers/dri/i965/brw_vec4.cpp | 11 +++++++----
>>>>>>>  2 files changed, 16 insertions(+), 8 deletions(-)
>>>>>>>
>>>>>>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
>>>>>>> index 29f19cc..9520a62 100644
>>>>>>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>>>>>>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>>>>>>> @@ -4947,6 +4947,8 @@ fs_visitor::calculate_register_pressure()
>>>>>>>  void
>>>>>>>  fs_visitor::optimize()
>>>>>>>  {
>>>>>>> +   static int global_iteration = 0;
>>>>>>
>>>>>> I don't know that adding a static variable is the way to solve this. I
>>>>>> know this is debugging code, but using a static variable will make
>>>>>> this thread-unsafe, and I *really* don't want to end up in a situation
>>>>>> where I can't figure out what the optimizer is doing because we were
>>>>>> compiling shaders in parallel...
>>>>>
>>>>> If we really care, we can use an atomic, but meh.  How often are you
>>>>> seriously using INTEL_DEBUG=optimizer on something that's compiling
>>>>> enough shaders in parallel for this to realistically be a problem?  I
>>>>> wouldn't want to dig through that many results.  But, like I said, if
>>>>> it bothers you, make it an atomic.
>>>>
>>>> That doesn't help.
>>>
>>> Then what thread-saftey issue are you concerned with here?
>>
>> The code *reads* a global variable that might be changed by another
>> thread during the first thread's optimization loop.
>
> Right.  I didn't pay that much attention to the exact implementation.
> But we could do something like.
>
> atomic int global_iteration_atomic = 0;
>
> const int global_iteration = atomic_inc(global_iteration_atomic);
>
> // use global_iteration everywhere

Yeah, that should work.