Re: [boost] interest in structure of arrays container?

Subject: Re: [boost] interest in structure of arrays container?
From: Larry Evans (cppljevans_at_[hidden])
Date: 2016-10-30 08:45:12

Michael, the latest revision of the code, when run, aborts when
running the SSEopt_vec method, as detailed here:

https://github.com/cppljevans/soa/blob/master/soa_compare.benchmark.cpp#L953

Would you have some idea what's causing that?

On 10/28/2016 09:40 PM, Michael Marcin wrote:
> On 10/28/2016 9:09 AM, Larry Evans wrote:
>> On 10/26/2016 10:00 AM, Michael Marcin wrote:
>> [snip]
>>>
>>> The sse emitter test used an aligned_allocator to guarantee 16 byte
>>> alignment for the std::vector data.
>>>
>>>     template< typename T >
>>>     using sse_vector = vector<T, aligned_allocator<T,16> >;
>>>
>> I assume that vector<T>'s data is allocated with new,
>> and new, IIUC, guarantees maximum alignment; hence,
>>   boost::alignment::is_aligned(std::vector<T>::data(),16)
>> should always be true.  What am I missing?
>
>
> Yes operator new isn't going to guarantee a 16 byte alignment on any
> platform I'm aware of.
>
> From n4606
[snip] Detailed reference to standard Docs correcting my assumptions.

Thanks for the [snipped] detailed reference to standard Docs correcting
my assumptions :)  It must have taken a lot of detailed reading!

>>
>> BTW, see the new push:
>>
>> https://github.com/cppljevans/soa/commit/ea28ff814c8c1ea879fa5ac2453c12fc382ad17f
>>
>>
>>
>> I've *not tested* it in:
>>
>>   https://github.com/cppljevans/soa/blob/master/soa_compare.benchmark.cpp
>>
>> but I think it should work.

Since that post, I've actually tested with the benchmark, and it ran.
That run was done with the previous revision, the one with:

https://github.com/cppljevans/soa/commit/02791e47080bf51ac3a467ed89e7cb91abf3a966

Strangely, that one ran the SSEopt_vec method OK, in constrast
to the current SSEopt_vec method.

 >> IOW, instead of:
>>
>>     sse_vector<float> position_x;
>>     sse_vector<float> position_y;
>>     sse_vector<float> position_z;
>>     sse_vector<float> velocity_x;
>>     sse_vector<float> velocity_y;
>>     sse_vector<float> velocity_z;
>>     sse_vector<float> acceleration_x;
>>     sse_vector<float> acceleration_y;
>>     sse_vector<float> acceleration_z;
>>     vector<float2> size;
>>     vector<float4> color;
>>     sse_vector<float>  energy;
>>     vector<char>   alive;
>>
>> I think you could use:
>>
>>       soa_block
>>       <
>>         type_align<float,16>,// position_x;
>>         type_align<float,16>,// position_y;
>>         type_align<float,16>,// position_z;
>>         type_align<float,16>,// velocity_x;
>>         type_align<float,16>,// velocity_y;
>>         type_align<float,16>,// velocity_z;
>>         type_align<float,16>,// acceleration_x;
>>         type_align<float,16>,// acceleration_y;
>>         type_align<float,16>,// acceleration_z;
>>         float2_t,// size;
>>         float4_t,// color;
>>         type_align<float,16>,// energy;
>>         char// alive;
>>       > particles;
>>
>> where type_align is found here:
>>
>> https://github.com/cppljevans/soa/blob/master/vec_offsets.hpp#L14
>>
>
> That's quite similar to what I have in one of my potential implementations.
>

Would you post that somewhere?  I'd be curious about how it
differs.

-regards,
Larry