I can generate synthetic files of 40,000 and 400,000 lines with 50 samples per line and process them in around 2 minutes 18 seconds on a reasonable 4 core (+hyperthreading) desktop iMac in my clumsy style of C++ without any SIMD optimisation (by me) using GNU Parallel.
Here is the top-level script. You can see it generates the test data in "a.txt" and "b.txt". Then it "compresses" "b.txt" to an identical binary representation, with the pre-computed magnitude appended to each line. Finally, it numbers the lines in "a.txt" and passes them into GNU Parallel which splits the lines into groups of around 5,200 lines and starts a group of 8 parallel processes to compare each of those lines with the 40,000 lines in B.
#!/bin/bash
# Generate test data - a.txt b.txt
./generate
# Preprocess b.txt into binary with precomputed magitudes save as B
./preprocess
# Process file A in batches
cat -n a.txt | parallel --block-size 2M --line-buffer --pipe ./process {#}
Here is the generate.cpp program to synthesise data:
#include <iostream>
#include <cstdlib>
#include <fstream>
#include "common.h"
using namespace std;
int main()
{
int line,sample;
ofstream a("a.txt");
if (!a.is_open()){
cerr << "ERROR: Unable to open output file";
exit(EXIT_FAILURE);
}
for(line=0;line<ALINES;line++){
for(sample=0;sample<SAMPLESPERLINE;sample++){
a << (float)rand()*100/RAND_MAX << " ";
}
a << endl;
}
a.close();
ofstream b("b.txt");
if (!b.is_open()){
cerr << "ERROR: Unable to open output file";
exit(EXIT_FAILURE);
}
for(line=0;line<BLINES;line++){
for(sample=0;sample<SAMPLESPERLINE;sample++){
b << (float)rand()*100/RAND_MAX << " ";
}
b << endl;
}
b.close();
}
Here is the preprocess.cpp code:
#include <sstream>
#include <fstream>
#include <string>
#include <iostream>
#include <stdlib.h>
#include <vector>
#include <cmath>
#include "common.h"
int main(int argc, char* argv[]){
std::ifstream btxt("b.txt");
std::ofstream bbin("B",std::ios::out|std::ios::binary);
if (!btxt.is_open()){
std::cerr << "ERROR: Unable to open input file";
exit(EXIT_FAILURE);
}
if (!bbin.is_open()){
std::cerr << "ERROR: Unable to open output file";
exit(EXIT_FAILURE);
}
int l=0;
std::string line;
std::vector<float> v;
v.resize(SAMPLESPERLINE+1);
while (std::getline(btxt,line)){
std::istringstream iss(line);
v.clear();
float f;
double magnitude;
magnitude=0.0;
int s=0;
while (iss >> f){
v[s]=(f);
magnitude+=(double)f*f;
s++;
}
// Append the magnitude to the end of the "line"
v[s]=(float)sqrt(magnitude);
// Write the samples and magnitide in binary to the output file
bbin.write(reinterpret_cast<char*>(&v[0]),(SAMPLESPERLINE+1)*sizeof(float));
l++;
}
btxt.close();
bbin.close();
return EXIT_SUCCESS;
}
Here is the common.h file:
const int ALINES=400000;
const int BLINES=40000;
const int SAMPLESPERLINE=50;
And here is the process.cpp code:
#include <sstream>
#include <fstream>
#include <string>
#include <iostream>
#include <stdlib.h>
#include <vector>
#include <array>
#include <cmath>
#include "common.h"
int main(int argc, char* argv[]){
if(argc!=2){
std::cerr << "Usage: process JOBNUM" << std::endl;
exit(1);
}
int JobNum=std::atoi(argv[1]);
std::cerr << "Starting job: " << JobNum << std::endl;
// Load B
std::ifstream bbin("B",std::ios::binary);
if (!bbin.is_open()){
std::cerr << "ERROR: Unable to open B";
exit(EXIT_FAILURE);
}
int l=0;
std::array<float,SAMPLESPERLINE+1> record;
std::vector<std::array<float,SAMPLESPERLINE+1>> B;
B.resize(BLINES);
for(l=0;l<BLINES;l++){
// Read one record of 50 floats and their magnitude
bbin.read(reinterpret_cast<char*>(&B[l][0]),sizeof(float)*(SAMPLESPERLINE+1));
}
bbin.close();
// Process all lines read from stdin, each line prepended by its line number
// Format is:
// <line number in file "a.txt"> <SAMPLE0> <SAMPLE1> ... <SAMPLE49>
int nLines=0;
std::string line;
while (std::getline(std::cin,line)){
nLines++;
std::istringstream iss(line);
std::vector<float> A;
A.resize(SAMPLESPERLINE);
float f;
int Alineno;
int s=0;
iss >> Alineno;
double dMag=0.0;
while (iss >> f){
A[s++]=f;
dMag+=(double)f*f;
}
// Root magnitude
float AMagnitude=(float)sqrt(dMag);
// At this point we have in B, 40,000 records each of 50 samples followed by the magnitude
// ... and we have a single record from "a.txt" with 50 samples and its magnitude in AMagnitude
// ... and Alineno is the absolute line number in "a.txt" of this line
// Time to do the actual calculation: compare this record to all records in B
for(int brec=0;brec<BLINES;brec++){
float BMagnitude=B[brec][SAMPLESPERLINE];
double dotproduct=0.0;
float *a = &A[0];
float *b = &B[brec][0];
for(s=0;s<SAMPLESPERLINE;s++){
dotproduct += (*a++) * (*b++);
}
float similarity = dotproduct/(AMagnitude*BMagnitude);
if(similarity>0.99){
std::cout << "Line A: " << Alineno << ", line B: " << brec << ", similarity:" << similarity << std::endl;
}
}
}
std::cerr << "Ending job: " << JobNum << ", processed " << nLines << " lines" << std::endl;
return EXIT_SUCCESS;
}
The Makefile is pretty simple:
CFLAGS= -std=c++11 -O3 -march=native
all: generate preprocess process
generate: generate.cpp
clang++ ${CFLAGS} generate.cpp -o generate
preprocess: preprocess.cpp
clang++ ${CFLAGS} preprocess.cpp -o preprocess
process: process.cpp
clang++ ${CFLAGS} process.cpp -o process
When you run it, it pegs the CPU for 2 minutes and looks like this:
time ./go
Starting job: 3
Starting job: 7
Starting job: 8
Starting job: 2
Starting job: 5
Starting job: 1
Starting job: 4
Starting job: 6
Ending job: 1, processed 5204 lines
Starting job: 9
Ending job: 2, processed 5203 lines
Ending job: 3, processed 5204 lines
Starting job: 11
Starting job: 10
Ending job: 4, processed 5204 lines
Starting job: 12
Ending job: 5, processed 5203 lines
Ending job: 6, processed 5203 lines
Starting job: 14
Starting job: 13
...
...
Starting job: 75
Ending job: 68, processed 5204 lines
Ending job: 69, processed 5203 lines
Starting job: 76
Starting job: 77
Ending job: 70, processed 5203 lines
Ending job: 71, processed 5204 lines
Ending job: 72, processed 5203 lines
Ending job: 77, processed 4535 lines
Ending job: 74, processed 5204 lines
Ending job: 73, processed 5205 lines
Ending job: 75, processed 5204 lines
Ending job: 76, processed 5203 lines
real 2m17.510s
user 16m24.533s
sys 0m4.426s
Note that I have not done any explicit SIMD or loop-unrolling or used any intrinsics to form the dot-product. I suspect if you asked a question about forming a dot-product and tagged it with simd or avx, someone would help you optimise it.
Note also that you could easily run this code across multiple computers with GNU Parallel, assuming you have ssh login to them, just using:
parallel -S host1,host2,host3 ....
For example, I have a 6-core Debian PC on my network, so I ran the above code parallelised across my 4-core Mac and 6-core Debian machine with:
parallel -S :,debian ...
and it then takes 1 minute 8 seconds.
