[Mesa-dev] [PATCH 3/3] radeonsi: use #pragma pack to pack si_shader_key

[Nicolai Hähnle]

On 27.06.2017 00:15, Marek Olšák wrote:
> On Thu, Jun 22, 2017 at 9:19 AM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
>> On 20.06.2017 20:00, Marek Olšák wrote:
>>>
>>> From: Marek Olšák <marek.olsak at amd.com>
>>>
>>> sizeof(struct si_shader_key):
>>>     Before reverting the 2 commits: 120 bytes
>>>     After reverting the 2 commits: 128 bytes
>>>     With #pragma pack: 107 bytes
>>>
>>> I'm not sure if memcmp with a byte-aligned size is a good idea.
>>
>>
>> Does this have a measurable impact? The code is nicer to read with the
>> structure after the patches, but I'm not sure it's worth the risk of getting
>> misaligned data somewhere.
> 
> It decreases the time spent in si_update_shaders by 6% when going from
> 128 bytes to 106 for the shader key.
> 
> What do you mean by the risk?

If we end up accidentally misaligning a member, that could cause a 
performance hit. But those 6% improvement does seem worth it. I do think 
Emil's suggestion of adding the attribute directly to the structures is 
a good idea. With that, the patch is

Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>


> 
> Marek
> 


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