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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <25289.1568379639@warthog.procyon.org.uk>
References: <25289.1568379639@warthog.procyon.org.uk>
To:     torvalds@linuxfoundation.org
Cc:     dhowells@redhat.com, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: My just-shovel-data-through-for-X-amount-of-time test
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Date:   Fri, 13 Sep 2019 14:06:39 +0100
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/*
 * Benchmark a pipe by seeing how many 511-byte writes can be stuffed through
 * it in a certain amount of time.  Compile with -lm.
 */
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <math.h>
#include <sys/wait.h>
#include <sys/mman.h>

static char buf1[4096] __attribute__((aligned(4096)));
static char buf2[4096] __attribute__((aligned(4096)));
static unsigned long long *results;

static volatile int stop;
void sigalrm(int sig)
{
	stop = 1;
}

static __attribute__((noreturn))
void producer(int fd, int i)
{
	unsigned long long l = 0;
	ssize_t n;

	signal(SIGALRM, sigalrm);
	alarm(1);

	while (!stop) {
		n = write(fd, buf1, 511);
		if (n == -1) {
			perror("read");
			exit(1);
		}

		l += n;
	}

	results[i] = l;
	exit(0);
}

static __attribute__((noreturn))
void consumer(int fd)
{
	unsigned long long l = 0;
	ssize_t n;

	for (;;) {
		n = read(fd, buf2, 4096);
		if (n == 0)
			break;
		if (n == -1) {
			perror("read");
			exit(1);
		}

		l += n;
	}

	exit(0);
}

unsigned long long stddev(const unsigned long long *vals, int nvals)
{
	double sum = 0.0, mean, sd = 0.0;
	int i;

	for (i = 0; i < nvals; i++)
		sum += vals[i];

	mean = sum / nvals;
	for (i = 0; i < nvals; i++)
		sd += pow(vals[i] - mean, 2);
	return sqrt(sd / 10);
}

int main()
{
	unsigned long long t = 0;
	int ex = 0, i;

	results = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);
	if (results == MAP_FAILED) {
		perror("mmap");
		exit(1);
	}

	for (i = 0; i < 16 && ex == 0; i++) {
		pid_t prod, con;
		int pfd[2], wt;

		if (pipe2(pfd, 0) < 0) {
			perror("pipe");
			exit(1);
		}

		con = fork();
		switch (con) {
		case -1:
			perror("fork/c");
			exit(1);
		case 0:
			close(pfd[1]);
			consumer(pfd[0]);
		default:
			break;
		}

		prod = fork();
		switch (prod) {
		case -1:
			perror("fork/p");
			exit(1);
		case 0:
			close(pfd[0]);
			producer(pfd[1], i);
		default:
			break;
		}

		close(pfd[0]);
		close(pfd[1]);

		for (;;) {
			errno = 0;
			wait(&wt);
			if (errno == ECHILD)
				break;
			if (!WIFEXITED(wt) || WEXITSTATUS(wt) != 0)
				ex = 1;
		}

		printf("WR[%02u]: %12llu\n", i, results[i]);
		t += results[i];
	}

	printf("total : %12llu\n", t);
	printf("avg   : %12llu\n", t / i);
	printf("stddev: %12llu\n", stddev(results, i));
	exit(ex);
}