dst.c

#include "main.h"
#include <errno.h>

int main(int argc, char *argv[])
{
    unsigned long long len;
    unsigned long long ret = -1;
    int fd;
    char *buf;
    char buf_args[50];
    clock_t begin, end;
    double time_spent;
    struct iovec local[1], remote[1];
    pid_t rpid;

    fd = open(NAME, O_RDONLY);
    if (fd < 0) {
	    printf("Failed to open "NAME"\n");
	    exit(1);
    }
    read(fd, buf_args, 50);
    close(fd);

    if ((sscanf(buf_args, "%lld %p %d",
            &len, &(remote->iov_base), &rpid)) != 3) {
        printf("Invalid args\n");
        exit(1);
    }

    buf = malloc(len * sizeof(char));
    if (buf == NULL) {
		printf("No memory: %lld\n", len);
		goto out;
    }

    local->iov_base = buf;
    local->iov_len = len;
    remote->iov_len = len;

    begin = clock();

    while(local->iov_len !=0 &&
	    (ret = process_vm_readv(rpid, local, 1, remote, 1, 0)) != 0) {
	    if (ret == -1) {
		    if (errno == EINTR)
			    continue;
		    perror("process_vm_readv");
		    goto out;
	    }

	    local->iov_base += ret;
	    remote->iov_base += ret;
	    local->iov_len -= ret;
	    remote->iov_len -= ret;
    }

    end = clock();
    time_spent = (double)(end - begin) / CLOCKS_PER_SEC;

    printf("len = %s\tread time:\t%f\n", get_size(len), time_spent);

    ret = 0;

 out:
    kill(rpid, SIGKILL);
    unlink(NAME);
    return ret;
}

main.h

#define _GNU_SOURCE
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <sys/uio.h>
#include <sys/types.h>
#include <sys/stat.h>

#define NAME "testfifo"

char *get_size(size_t  size)
{
    static const char *SIZES[] = {"B", "kB", "MB", "GB"};
    size_t div = 0;
    size_t rem = 0;
    char *buf;

    buf = malloc(50 * sizeof(char));

    while (size >= 1024 &&
            div < (sizeof(SIZES)/sizeof(*SIZES))) {
        rem = (size % 1024);
        div++;
        size /= 1024;
    }

    snprintf(buf, 50, "%.1f %s",
        (float)size + (float)rem / 1024.0,
        SIZES[div]);
    return buf;
}

Makefile

all: build run

build:
	gcc -Wall dst.c -o dst
	gcc -Wall src.c -o src

run: t1 t2 t3 t4 t5 t6 t7 t8
	cat *.log >> results.txt
	rm -f *.log

t1:
	setsid ./src 1 &
	sleep 1
	sudo ./dst >> t1.log
t2:
	setsid ./src 2 &
	sleep 1
	sudo ./dst >> t2.log
t3:
	setsid ./src 3 &
	sleep 1
	sudo ./dst >> t3.log
t4:
	setsid ./src 4 &
	sleep 1
	sudo ./dst >> t4.log
t5:
	setsid ./src 5 &
	sleep 1
	sudo ./dst >> t5.log
t6:
	setsid ./src 6 &
	sleep 1
	sudo ./dst >> t6.log
t7:
	setsid ./src 7 &
	sleep 1
	sudo ./dst >> t7.log
t8:
	setsid ./src 8 &
	sleep 1
	sudo ./dst >> t8.log

clean:
	rm -f src dst *.log

results.txt

len = 256.0 MB	read time:	0.057027
len = 512.0 MB	read time:	0.112965
len = 768.0 MB	read time:	0.169697
len = 1.0 GB	read time:	0.224373
len = 1.2 GB	read time:	0.278507
len = 1.5 GB	read time:	0.333400
len = 1.8 GB	read time:	0.393584
len = 2.0 GB	read time:	0.459082

src.c

#include "main.h"

int main(int argc, char *argv[])
{
    unsigned long long len = 256 * 1024 * 1024;
    int fd;
    char dst_args[50];
    unsigned dst_args_len;
    char *buf;

    if (argc != 2) {
        printf("Usage: %s <BUFFER_LENGTH>\n", argv[0]);
        exit(1);
    }
    unlink(NAME);
    mkfifo(NAME, 0666);
    len *= atoi(argv[1]);
    buf = malloc(len * sizeof(char));
    dst_args_len = sprintf(dst_args, "%lld %p %d\n", len, buf, getpid());

    fd = open(NAME, O_WRONLY);
    write(fd, dst_args, dst_args_len);
    close(fd);

    for (int i = 0; i < len; ++i)
        buf[i] = (i % 26) + 'A';
    buf[len] = '\0';

    while(1)
        sleep(1);

    return 0;
}