linux signals benchmarking

signals.c

#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <time.h>
#include <unistd.h>
#include <signal.h>
#include <ucontext.h>
#include <fcntl.h>
#include <execinfo.h>
#include <sys/mman.h>

#define PAGE_SIZE sysconf(_SC_PAGESIZE)
#define PAGE_MASK (PAGE_SIZE - 1)
#define PAGE_ALIGN_DOWN(x) (((intptr_t) (x)) & ~PAGE_MASK)
#define N (PAGE_SIZE/sizeof(uint64_t))
#define NTIMES 1ULL<<22

static uint64_t remaining;

void initialize(uint64_t *a, size_t size) {
	printf("initializing... ");
	fflush(stdout);
	clock_t start = clock();
	a[0] = 123;
	for (size_t i=1; i < size; i++) {
		a[i] = a[i-1] * a[i-1] % 100000;
	}
	clock_t end = clock();
	double seconds = (double)(end - start) / CLOCKS_PER_SEC;
	printf("done in %lf seconds\n", seconds);
}

void segv_handler(int signum, siginfo_t *siginfo, void *ctx) {
	if (--remaining == 0) {
		mprotect((void*) PAGE_ALIGN_DOWN(siginfo->si_addr),
		         PAGE_SIZE, PROT_READ | PROT_WRITE);
	}
}

void install_sighandler() {
	stack_t sigstk;
	sigstk.ss_sp = malloc(SIGSTKSZ);
	sigstk.ss_size = SIGSTKSZ;
	sigstk.ss_flags = 0;
	sigaltstack(&sigstk, NULL);
	struct sigaction siga;
	sigemptyset(&siga.sa_mask);
	sigaddset(&siga.sa_mask, SIGSEGV);
	// block signals temporarily
	sigprocmask(SIG_BLOCK, &siga.sa_mask, NULL);
	siga.sa_flags = SA_SIGINFO | SA_ONSTACK | SA_RESTART | SA_NODEFER;
	// install segv handler
	siga.sa_sigaction = segv_handler;
	if (sigaction(SIGSEGV, &siga, NULL) == -1) {
		fprintf(stderr, "error installing sigsegv handler\n");
		exit(-1);
	}
	sigprocmask(SIG_UNBLOCK, &siga.sa_mask, NULL);
}

void time_signals(uint64_t *a, size_t size, size_t ntimes) {
	remaining = ntimes;
	mprotect(a, PAGE_SIZE, PROT_READ);
	clock_t start = clock();
	a[1] = a[2] + a[3];
	clock_t end = clock();
	double seconds = (double)(end - start) / CLOCKS_PER_SEC;
	printf("%zu signals -> %lf seconds\n", ntimes, seconds);
}

int main() {
	uint64_t *a = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE,
	                   MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	install_sighandler();
	initialize(a, N);
	for (int i=1; i <= NTIMES; i *= 2) {
		time_signals(a, 100, i);
	}
	return 0;
}