[PATCH 2/6] d3dx9: Use versioned parameter updates instead of 'dirty' flags.

[Paul Gofman]

On 05/15/2017 09:19 PM, Matteo Bruni wrote:
> 2017-05-12 14:24 GMT+02:00 Paul Gofman <gofmanp at gmail.com>:
>
>
>> @@ -163,6 +163,7 @@ struct d3dx_const_tab
>>       unsigned int const_set_size;
>>       struct d3dx_const_param_eval_output *const_set;
>>       const enum pres_reg_tables *regset2table;
>> +    ULONG64 update_version;
>>   };
> Is it necessary? Could you do without it, using the pass version instead?
I think I can, but the reasons I did this were:
1. The logic in patch 5 (removing redundant constant table updates & 
preshader recomputes) won't work without it. Imagine an array selector 
with shader 1 selected, when after BeginPass() or Commit() it will 
update the version of pass. If another shader is selected later it might 
not get updated for the some parameter changes, so I will have to 
ultimately recompute all preshaders and reset constant table parameters 
on update_all, which I can avoid using this const_tab own version. Even 
if I manage to workaround this case with array selector somehow, 
redundant shader constant updates and preshaders recomputes can happen 
if different passes or techniques use the same shader (as preshader 
functions will be called with some old update_version, older than the 
last one for which this was actually called already).
     So I guess going without would mean abandoning the idea for patch 
5, or somehow greatly complicating it.

2. I thought encapsulating constant updates arguably makes (for 
everything but a very specific case of emulating native behaviour on 
array selector index) it more structural and easier verifiable. It is 
just a single value for the whole parameter table, so I didn't think it 
should add an overhead compared to passing the parameter.

3. Adding 'update_version' parameter to (almost) every preshader.c 
function call looked more ugly to me.
>>   struct d3dx_shared_data;
>>
>> @@ -213,6 +214,8 @@ struct d3dx_parameter
>>       UINT bytes;
>>       DWORD runtime_flags;
>>       DWORD object_id;
>> +    ULONG64 update_version;
>> +    ULONG64 *update_version_counter;
> I don't like the "update_version_counter" name that much but I don't
> have particularly good suggestions. pass_update_version?
> current_update_version? parent_update_version? new_update_version?
It is not a pass update version in my understanding, it relates to 
parameter or constant table update version as well. So maybe 
current_update_version? Or just version_counter, which looks consistent 
to how the same thing is often named in DBs?
>
>> +static inline ULONG64 get_update_version_counter(ULONG64 *update_version_counter)
>> +{
>> +    return ++*update_version_counter;
>> +}
> Maybe it's just me but it's a bit surprising to see this get_x()
> function having side effects. Not sure how to call it.
> next_update_version()? inc_update_version_counter()?
I will rename to next_update_version().
>
>> +static inline BOOL is_param_dirty(struct d3dx_parameter *param, ULONG64 update_version)
>> +{
>> +    struct d3dx_shared_data *shared_data;
>> +
>> +    if ((shared_data = param->top_level_param->u.shared_data))
>> +        return update_version < shared_data->update_version;
>> +    else
>> +        return update_version < param->top_level_param->update_version;
>> +}
> Did you try if a unified update_version pointer looks any nicer?
> Especially considering that you have a more or less matching
> *update_version_counter at the moment.
Do you mean a pointer in the update_version in the struct d3dx_parameter 
which will point to either shared data or the update version in the same 
parameter? I would like to avoid this if possible as it makes extra 
indirection for non-shared parameters. I don't have exact performance 
difference exactly for such a change though, but it looks like removing 
some indirections here and there (after a more global optimizations of 
set_constants function) gives some moderate improvement.

     In the further optimization which I am testing I go bit more 
towards less indirection, e. g., in function is_const_tab_input_dirty() 
I use the fact that actually the parameters there are always top level.
>
>>   HRESULT d3dx_evaluate_parameter(struct d3dx_param_eval *peval,
>> -        const struct d3dx_parameter *param, void *param_value, BOOL update_all) DECLSPEC_HIDDEN;
>> +        const struct d3dx_parameter *param, void *param_value) DECLSPEC_HIDDEN;
> I guess this has to do with the update_version in struct
> d3dx_const_tab. I might be missing something, in that case please clue
> me.
I don't need update_all parameter anymore here (regardless of storing 
update_version), as I don't have to ever recompute preshader for 
parameter if it is not required by parameter version change.
If update_version is stored d3dx_const_tab, I don't have to pass an 
update_version here, apart from some other benefits I see in that as I 
outlined above. Otherwise I need to pass a version as a parameter to 
this function.

>> +static ULONG64 get_effect_update_version_counter(struct d3dx9_base_effect *base)
>> +{
>> +    return get_update_version_counter(get_update_version_counter_ptr(base));
>>   }
> Same naming caveat here.
next_effect_update_version()?
>
>> -static void clear_dirty_params(struct d3dx9_base_effect *base)
>> +static void set_dirty(struct d3dx_parameter *param)
>>   {
>> -    unsigned int i;
>> +    struct d3dx_shared_data *shared_data;
>> +    struct d3dx_parameter *top_param = param->top_level_param;
>> +    ULONG64 new_update_version = get_update_version_counter(top_param->update_version_counter);
>>
>> -    for (i = 0; i < base->parameter_count; ++i)
>> -        base->parameters[i].runtime_flags &= ~PARAMETER_FLAG_DIRTY;
>> +    if ((shared_data = top_param->u.shared_data))
>> +        shared_data->update_version = new_update_version;
>> +    else
>> +        top_param->update_version = new_update_version;
>>   }
> Another option would be NOT to increment the effect / pool counter on
> each set_dirty() but instead only increment it in BeginPass() and
> CommitChanges(), after you're done with the update (or well, it's fine
> at almost any point given that we don't have to care about races). It
> seems a bit better to me, unless I'm overlooking something and it
> won't work.
     After this patch, set_dirty() is already completely out of any 
performance hot spots, as far as I could measure so far (though there 
are the other places like mainly set_constants that I was going to 
address too).

     Not incrementing the version does not improve things much in terms 
of racing in my understanding. Since we don't have to support it within 
pool it should be ok either way. If we had to, we would also need to 
care for some way for atomic & fenced read even when not incrementing, 
and probably parallel BeginPass with Set... would make non-incrementing 
logic require additional sync.

     Not incrementing the version on update likely won't break anything, 
if to change the initialization a bit (increment version on effect 
creation) and carefully watch comparison condition for a sort of "off by 
one" errors. At least now I cannot figure out what can go wrong, though 
I need to test it more and to recheck the code paths thoroughly to be 
sure if it is ok. It looked natural to me to increase the version on 
parameter update. Don't you think that verifying the overall logic if we 
don't increment becomes a bit mind breaking? Incrementing the version 
every time makes the 'updated' check straightforward for any case, 
regardless of how parameters update sequence interfere with updates 
'consuming' sequence. Otherwise we need to check all the possible use 
cases of "dirty" parameters to be sure.

     Or if you suspect it may have some indirect performance impact 
(which I am keen to test) maybe I could test it as a separate change 
after some other (more severe) optimization, when I potentially can see 
this effect more clear?