Ensure the flush overhead stays below 1 ms

Uses /dev/shm as temporary directory.

test/CMakeLists.txt

@@ -21,6 +21,11 @@ target_link_libraries(flush ovni)
 add_test(NAME flush COMMAND "${OVNI_TEST_DIR}/driver.sh" flush)
 set_tests_properties(flush PROPERTIES RUN_SERIAL TRUE)
 
+add_executable(flush-overhead flush-overhead.c)
+target_link_libraries(flush-overhead ovni)
+add_test(NAME flush-overhead COMMAND "${OVNI_TEST_DIR}/driver.sh" flush-overhead)
+set_tests_properties(flush-overhead PROPERTIES RUN_SERIAL TRUE)
+
 add_executable(mp-simple mp-simple.c)
 target_link_libraries(mp-simple ovni)
 add_test(NAME mp-simple COMMAND "${OVNI_TEST_DIR}/mp-driver.sh" mp-simple)

test/flush-overhead.c

@@ -0,0 +1,116 @@
+/*
+ * Copyright (c) 2021-2022 Barcelona Supercomputing Center (BSC)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#define _POSIX_C_SOURCE 200112L
+#define _GNU_SOURCE
+
+#include <stdint.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <linux/limits.h>
+#include <limits.h>
+
+#include "ovni.h"
+#include "compat.h"
+
+static inline void
+init(void)
+{
+	char hostname[HOST_NAME_MAX];
+
+	if(gethostname(hostname, HOST_NAME_MAX) != 0)
+	{
+		perror("gethostname failed");
+		exit(EXIT_FAILURE);
+	}
+
+	ovni_proc_init(0, hostname, getpid());
+	ovni_thread_init(gettid());
+	ovni_add_cpu(0, 0);
+}
+
+static void emit(uint8_t *buf, size_t size)
+{
+	struct ovni_ev ev = {0};
+	ovni_ev_set_mcv(&ev, "O$$");
+	ovni_ev_set_clock(&ev, ovni_clock_now());
+	ovni_ev_jumbo_emit(&ev, buf, size);
+}
+
+#define NRUNS 50
+
+int main(void)
+{
+	size_t payload_size;
+	uint8_t *payload_buf;
+
+	if(setenv("OVNI_TMPDIR", "/dev/shm/ovni-flush-overhead", 1) != 0)
+	{
+		perror("setenv failed");
+		exit(EXIT_FAILURE);
+	}
+
+	init();
+
+	payload_size = (size_t) (0.5 * (double) OVNI_MAX_EV_BUF);
+	payload_buf = calloc(1, payload_size);
+
+	if(!payload_buf)
+	{
+		perror("calloc failed");
+		exit(EXIT_FAILURE);
+	}
+
+	double *times = calloc(sizeof(double), NRUNS);
+	if(times == NULL)
+	{
+		perror("calloc failed");
+		exit(EXIT_FAILURE);
+	}
+
+	for(int i=0; i < NRUNS; i++)
+	{
+		emit(payload_buf, payload_size);
+		double t0 = (double) ovni_clock_now();
+		ovni_flush();
+		double t1 = (double) ovni_clock_now();
+
+		times[i] = (t1 - t0) * 1e-6; /* to milliseconds */
+	}
+
+	double mean = 0.0;
+	for(int i=0; i < NRUNS; i++)
+		mean += times[i];
+	mean /= (double) NRUNS;
+	
+	fprintf(stderr, "mean %f ms\n", mean);
+
+	if (mean > 1.0) {
+		fprintf(stderr, "too much time: %f ms\n", mean);
+		exit(EXIT_FAILURE);
+	}
+
+	ovni_proc_fini();
+
+	free(payload_buf);
+	free(times);
+
+	return 0;
+}