Re: [ublas] Matrix multiplication performance

Subject: Re: [ublas] Matrix multiplication performance
From: Michael Lehn (michael.lehn_at_[hidden])
Date: 2016-02-02 17:26:08

I also started to write down some notes on the rational behind the micro-kernel:

http://www.mathematik.uni-ulm.de/~lehn/test_ublas/session6/page01.html

On 02 Feb 2016, at 21:43, Michael Lehn <michael.lehn_at_[hidden]> wrote:

> (So the pages are re-done …)
> 
> 
> 
> The bug is because NR is BlockSize<T>::NR divided by the vector length.  So this
> should work
> 
> //---------------------------------------------------------------------------------
> template <typename Index, typename T>
> typename std::enable_if<std::is_floating_point<T>::value,
> void>::type
> ugemm(Index kc, T alpha,
>                const T *A, const T *B,
>      T beta,
>      T *C, Index incRowC, Index incColC)
> {
>    A = (const T*) __builtin_assume_aligned (A, 128);
>    B = (const T*) __builtin_assume_aligned (B, 128);
>    static const unsigned div = 32/sizeof(T);
>    static const Index MR = BlockSize<T>::MR;
>    static const Index NR = BlockSize<T>::NR/div;
> 
>    typedef T vx __attribute__((vector_size (32)));
> 
>    vx P[MR*NR] __attribute__ ((aligned (128))) = {};
>    const vx *B_ = (vx *)B;
>    for (Index l=0; l<kc; ++l) {
>        for (Index i=0; i<MR; ++i) {
>            for (Index j=0; j<(NR); ++j) {
>                P[i * NR + j] += A[i]*B_[j];
>            }
>        }
>        A += MR;
>        B_ += NR;
>    }
> 
>    T *P_ = (T *)P;
>    for (Index j=0; j<NR*div; ++j) {
>        for (Index i=0; i<MR; ++i) {
>            C[i*incRowC+j*incColC] *= beta;
>            C[i*incRowC+j*incColC] += alpha*P_[i * NR * div + j];
>        }
>    }
> }
> //---------------------------------------------------------------------------------
> 
> However, as Karl pointed out it also should treat the case beta==0
> as a special case.
> 
> But I don’t get any speedup.  For the performance relevant is
> mainly the loop
> 
>    for (Index l=0; l<kc; ++l) {
>        for (Index i=0; i<MR; ++i) {
>            for (Index j=0; j<(NR); ++j) {
>                P[i * NR + j] += A[i]*B_[j];
>            }
>        }
>        A += MR;
>        B_ += NR;
>    }
> 
> From my experience, only if this is optimized to the extrem a little bit
> extra performance can be achieved by treating some special cases for
> the update
> 
>    T *P_ = (T *)P;
>    for (Index j=0; j<NR*div; ++j) {
>        for (Index i=0; i<MR; ++i) {
>            C[i*incRowC+j*incColC] *= beta;
>            C[i*incRowC+j*incColC] += alpha*P_[i * NR * div + j];
>        }
>    }
> 
> The main reason my code looks weird is that I also want to use it
> for teaching.  The way it is coded you easily can map it forth and
> back with the assembly code.
> 
> 
>> new kernel:
>> 
>> template <typename Index, typename T>
>> typename std::enable_if<std::is_floating_point<T>::value,
>> void>::type
>> ugemm(Index kc, T alpha,
>>                const T *A, const T *B,
>>      T beta,
>>      T *C, Index incRowC, Index incColC)
>> {
>>    A = (const T*) __builtin_assume_aligned (A, 128);
>>    B = (const T*) __builtin_assume_aligned (B, 128);
>>    static const unsigned div = 32/sizeof(T);
>>    static const Index MR = BlockSize<T>::MR;
>>    static const Index NR = BlockSize<T>::NR/div;
>> 
>>    typedef T vx __attribute__((vector_size (32)));
>> 
>>    vx P[MR*NR] __attribute__ ((aligned (128))) = {};
>>    const vx *B_ = (vx *)B;
>>    for (Index l=0; l<kc; ++l) {
>>        for (Index i=0; i<MR; ++i) {
>>            for (Index j=0; j<(NR); ++j) {
>>                P[i * NR + j] += A[i]*B_[j];
>>            }
>>        }
>>        A += MR;
>>        B_ += NR;
>>    }
>> 
>>    T *P_ = (T *)P;
>>    for (Index j=0; j<NR; ++j) {
>>        for (Index i=0; i<MR; ++i) {
>>            C[i*incRowC+j*incColC] *= beta;
>>            C[i*incRowC+j*incColC] += alpha*P_[i * NR + j];
>>        }
>>    }
>> }
> 
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