MPI实现fft的迭代算法 源于并行计算——结构。算法。编程中伪码 更新2

在实际使用中，更新1虽然看上去将计算和通信overlap了，但是，由于每次socket传输都会导致进入系统态，各种中断，更新cache，反而会很慢。而且，系统会对socket数量有限制。在我的实验环境中，以太网只允许开1k个socket，即单节点只能有1k个isend，这样严重妨碍了系统规模的扩大。所以，统一通信能获得更好的时间效果。更新通信方式。

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <sys/stat.h>
#include <memory.h>

typedef struct {
double real;
double img;
} com;

double PI;

int readBinary(char* file,void *buf,int fsize);//if named read causes override and miscall
int writeBinary(char *file,com *array,int size);
//don't use the omega array,not every node needs a whole copy of omega,not efficient
static inline void cp(com f,com *t);//copy complex
static inline void add(com a,com b,com* r);
static inline void mul(com a,com b,com* r);
static inline void sub(com a,com b,com* r);
int br(int src,int size);//bit reverse
void send(com *c,com *r,int s,int t);
void show(com a) {
printf("%.4f %.4f \n",a.real,a.img);
}
int main(int argc,char *argv[]) {
if(argc<3) {
printf("wtf\n");
return 1;
}
double st,et;
PI=atan(1)*4;
int self,size;//process id and total number of processes
MPI_Init(&argc,&argv);
st=MPI_Wtime();
MPI_Comm_rank(MPI_COMM_WORLD,&self);
MPI_Comm_size(MPI_COMM_WORLD,&size);
int fsize,n;
void *buf;
com *in;
if(0==self) {
//printf("start \n");
struct stat fstat;
stat(argv[1],&fstat);
fsize=fstat.st_size;
buf=malloc(fsize);
n=readBinary(argv[1],buf,fsize)/2;//n stands for total complex number
}
MPI_Bcast(&n,1,MPI_INT,0,MPI_COMM_WORLD);//every thread should know the total size

if(-1==n) {
printf("error reading \n");
MPI_Finalize();
}
in=(com*)malloc(n*sizeof(com));
if(0==self) {
memcpy(in,((int*)buf+1),n*sizeof(com));
free(buf);
}
int psize=n/size;
//data
com w,m;//omega
com t[psize];

int l=log(n)/log(2);

int off=self*psize;
//initialize data each round
MPI_Bcast(in,n*2,MPI_DOUBLE,0,MPI_COMM_WORLD);
for(int h=l-1;h>=0;--h) {
//calculate
int p=pow(2,h);
int q=n/p;
int k;
for(k=off;k<off+psize;++k) {
if(k%p==k%(2*p)) {
int time=p*(br(k,l)%q);
w.real=cos(2*PI*time/n);
w.img=sin(2*PI*time/n);
mul(in[k+p],w,&m);
add(in[k],m,&t[k-off]);
} else {
int time=p*(br(k-p,l)%q);
w.real=cos(2*PI*time/n);
w.img=sin(2*PI*time/n);
mul(in[k],w,&m);
sub(in[k-p],m,&t[k-off]);
}
}
MPI_Allgather(t,2*psize,MPI_DOUBLE,in,2*psize,MPI_DOUBLE,MPI_COMM_WORLD);
}
//MPI_Bcast(in,n*2,MPI_DOUBLE,0,MPI_COMM_WORLD);
//reverse all data
int rs=0;
for(int k=off;k<off+psize;++k) {//post all comunications first
//tag is always the sending row number
t[k-off]=in[br(k,l)];
}
MPI_Gather(t,psize*2,MPI_DOUBLE,in,psize*2,MPI_DOUBLE,0,MPI_COMM_WORLD);
if(0==self) {
/*		for(int i=0;i<n;++i) {
printf("b%d :%.4f %.4f \n",i,in[i].real,in[i].img);
}*/
writeBinary(argv[2],in,n);
}
free(in);
et=MPI_Wtime();
MPI_Finalize();
printf("%f \n",et-st);
return 0;
}

int readBinary(char* file,void *buf,int fsize) {
FILE *in;
if(!(in=fopen(file,"r"))) {
printf("can't open \n");
return -1;
}

fread(buf,sizeof(char),fsize,in);
int size=((int*)buf)[0];
fclose(in);
return size;
}

int writeBinary(char *file,com *array,int size) {
FILE *out;
if(!(out=fopen(file,"w"))) {
printf("can't open \n");
return -1;
}
int bsize=sizeof(int)+size*sizeof(com);
void *buf=malloc(bsize);
((int*)buf)[0]=2*size;
memcpy(((int*)buf+1),array,size*sizeof(com));
fwrite(buf,sizeof(char),bsize,out);
free(buf);
fclose(out);
return 0;
}
void cp(com f,com *t) {
t->real=f.real;
t->img=f.img;
}
void add(com a,com b,com *c)
{
c->real=a.real+b.real;
c->img=a.img+b.img;
}

void mul(com a,com b,com *c)
{
c->real=a.real*b.real-a.img*b.img;
c->img=a.real*b.img+a.img*b.real;
}
void sub(com a,com b,com *c)
{
c->real=a.real-b.real;
c->img=a.img-b.img;
}
int br(int src,int size) {
int tmp=src;
int des=0;
for(int i=size-1;i>=0;--i) {
des=((tmp&1)<<i)|des;
tmp=tmp>>1;
}
return des;
}

特别是在infiniband下，这个算法要快上十几倍。