Suggestion for vectorizing MaxPool and Convolution Layer

[Seyed Kian Mousavikia]

Hi everyone... I have been working on writing a CNN (convolutional neural network) code in vector intrinsic mode and it is finished but after examining my code I have found that convolution and max pool layers in vector mode are giving really bad latency and are much worse than their scaler counterpart...what I have done in vector mode is this:
I first sorted the input vector (sth like im2col) to have ordered input for my main convolution and max pool layer, and then since my filters are 2*2 in convolution and max pool I utilized vl=4 and then I used vwmul to multiply and vredsum to get the final answer of each convolution window (for max pool just vredmax).... Following is the code for my convolution:
Here is the sortging function(im2col):

void vec_Conv2d_in(signed char* in, signed short int inSizeCol, signed char* out, signed short int outSizeCol, int outSize) {
    int i = 0;
    int j = 0;
    int k = 0;
    int f = 1;
    signed short int m = outSizeCol;
    while (outSize != 0) {
        //////////////////
        out[j] = in[i];
        j++;
        i++;
        out[j] = in[i];
        j++;
        i = i + inSizeCol - 1;
        out[j] = in[i];
        j++;
        i++;
        out[j] = in[i];
        j++;
        ///////////////////
        m -= 2;
        if (m != 0) {
            k += 1;
            i = k;
        }
        else {
            i = inSizeCol * f;
            f++;
            k = i;
            m = outSizeCol;
        }
        outSize -= 4;
    }
}

And here is the main convolution:

void vec_conv2d(signed char* in, signed char* w1, signed char* w2, signed char* w3, signed char* w4, signed short int* out1, signed short int* out2, signed short int* out3, signed short int* out4, signed short int outSize) {
    signed short int j = 0;
    while (outSize != 0) {
        size_t vl = vsetvl_e8m1(4);
        vint8m1_t vin  = vle8_v_i8m1(in, vl);
        vint8m1_t vwc1 = vle8_v_i8m1(w1, vl);
        vint8m1_t vwc2 = vle8_v_i8m1(w2, vl);
        vint8m1_t vwc3 = vle8_v_i8m1(w3, vl);
        vint8m1_t vwc4 = vle8_v_i8m1(w4, vl);

        vint16m2_t vout1 = vwmul_vv_i16m2(vin, vwc1, vl);
        vint16m1_t vec_zero1 = vmv_v_x_i16m1(0, vl);
        vint16m1_t vec_sum1 = vredsum_vs_i16m2_i16m1(vec_zero1, vout1, vec_zero1, vl);
        out1[j] = vmv_x_s_i16m1_i16(vec_sum1);

        vint16m2_t vout2 = vwmul_vv_i16m2(vin, vwc2, vl);
        vint16m1_t vec_zero2 = vmv_v_x_i16m1(0, vl);
        vint16m1_t vec_sum2 = vredsum_vs_i16m2_i16m1(vec_zero2, vout2, vec_zero2, vl);
        out2[j] = vmv_x_s_i16m1_i16(vec_sum2);

        vint16m2_t vout3 = vwmul_vv_i16m2(vin, vwc3, vl);
        vint16m1_t vec_zero3 = vmv_v_x_i16m1(0, vl);
        vint16m1_t vec_sum3 = vredsum_vs_i16m2_i16m1(vec_zero3, vout3, vec_zero3, vl);
        out3[j] = vmv_x_s_i16m1_i16(vec_sum3);

        vint16m2_t vout4 = vwmul_vv_i16m2(vin, vwc4, vl);
        vint16m1_t vec_zero4 = vmv_v_x_i16m1(0, vl);
        vint16m1_t vec_sum4 = vredsum_vs_i16m2_i16m1(vec_zero4, vout4, vec_zero4, vl);
        out4[j] = vmv_x_s_i16m1_i16(vec_sum4);

        in += vl;
        outSize -= 1;
        j++;
    }
}

The main function:

int main() {
    long time1, time2;
    time1 = get_mcycle();
    signed char x[10000] = { ..... };
    signed char xp[39204]; //39204 = 99*99*4
    vec_Conv2d_in(x, 100, xp, 198, 39204); //198 = 99*2
    signed char wc11[4] = { 0b11110110,0b11011101,0b00100111,0b11110100 };
    signed char wc12[4] = { 0b00101110,0b11101011,0b11110011,0b11110100 };
    signed char wc13[4] = { 0b00011101,0b00001011,0b11100100,0b11011100 };
    signed char wc14[4] = { 0b00011001,0b00100110,0b11110100,0b00000100 };
    signed short int oc11[9801]; //9801 = 99*99
    signed short int oc12[9801]; //9801 = 99*99
    signed short int oc13[9801]; //9801 = 99*99
    signed short int oc14[9801]; //9801 = 99*99
    vec_conv2d(xp, wc11, wc12, wc13, wc14, oc11, oc12, oc13, oc14, 9801);
    time2 = get_mcycle();
    uart_printf("The operation took %d cycles\n\r", time2 - time1);
    asm volatile("jr x0;");
    return 0;
}

Note: Input is 100*100 matrix flattened to vector, the output will be 98*98 since the filter is 2*2 and stride is 1
Since it is worse than the scaler version, can you suggest a better coding algorithm for the vector convolution and max pool?

[Seyed Kian Mousavikia]

Hi @michael-platzer ... regarding the above issue I actually tried vector indexed load to eliminate the sorting function and hopefully get better letancy...
The code for maxpooling is sth like this:

void vec_maxPool(signed char* in1, signed short int inSizeCol, signed char* out1, signed short int n){
    signed short int j = 0;
    unsigned short int stride = 2;
    unsigned short int index[4] = { 0,1,inSizeCol,inSizeCol + 1 };
    size_t vl = vsetvl_e8m1(4);
    vuint16m2_t vindex = vle16_v_u16m2((const uint16_t*)index, vl);
    while (n > 0) {
        vint8m1_t vin1 = vloxei16_v_i8m1(in1, vindex, vl);
        vint8m1_t vec_zero1 = vmv_v_x_i8m1(0, vl);
        vint8m1_t vec_max1 = vredmax_vs_i8m1_i8m1(vec_zero1, vin1, vec_zero1, vl);
        out1[j] = vmv_x_s_i8m1_i8(vec_max1);
        vindex = vadd_vx_u16m2(vindex, stride, vl);
        n -= 1;
        j++;
    }
}

The code is not complete but at least for first element it should work.
I tested this with the following:
signed char in1[16] = { 11,2,1,3,76,19,22,0,18,0,1,90,42,10,0,11 }; //4*4 matrix flattened to 16 vector stride is 2 so output will be n=2*2
vec_maxPool(in1, 4, om1v, 4);
The ouput:
11,76,90,42
It is like normal loading 4 element and then vredmax ing the numbers....

11,2,1,3 ....>11
76,19,22,0 ....>76
18,0,1,90 ....>90
42,10,0,11 ....> 42

I tried other inputs and no index load is happening...
It is just like a normal load but I have written indexed load... Can you see my mistake?