[dpdk-dev] [PATCH 2/2] eal/windows: implement alarm API

[Dmitry Kozlyuk]

Implementation is based on waitable timers Win32 API. When timer is set,
a callback and its argument are supplied to the OS, while timer handle
is stored in EAL alarm list. When timer expires, OS wakes up the
interrupt thread and runs the callback. Upon completion it removes the
alarm.

Waitable timers must be set from the thread their callback will run in,
eal_intr_thread_schedule() provides a way to schedule asyncronuous code
execution in the interrupt thread. Alarm module builds synchronous timer
setup on top of it.

Windows alarms are not a type of DPDK interrupt handle and do not
interact with interrupt module beyond executing in the same thread.

Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk at gmail.com>
---
 lib/librte_eal/rte_eal_exports.def |   2 +
 lib/librte_eal/windows/eal_alarm.c | 219 +++++++++++++++++++++++++++++
 lib/librte_eal/windows/meson.build |   1 +
 3 files changed, 222 insertions(+)
 create mode 100644 lib/librte_eal/windows/eal_alarm.c

diff --git a/lib/librte_eal/rte_eal_exports.def b/lib/librte_eal/rte_eal_exports.def
index 9baca0110..b6abb5ae1 100644
--- a/lib/librte_eal/rte_eal_exports.def
+++ b/lib/librte_eal/rte_eal_exports.def
@@ -14,6 +14,8 @@ EXPORTS
 	rte_devargs_insert
 	rte_devargs_next
 	rte_devargs_remove
+	rte_eal_alarm_set
+	rte_eal_alarm_cancel
 	rte_eal_get_configuration
 	rte_eal_has_hugepages
 	rte_eal_has_pci
diff --git a/lib/librte_eal/windows/eal_alarm.c b/lib/librte_eal/windows/eal_alarm.c
new file mode 100644
index 000000000..3b262793a
--- /dev/null
+++ b/lib/librte_eal/windows/eal_alarm.c
@@ -0,0 +1,219 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright (c) 2020 Dmitry Kozlyuk
+ */
+
+#include <stdatomic.h>
+#include <stdbool.h>
+
+#include <rte_alarm.h>
+#include <rte_spinlock.h>
+
+#include <rte_eal_trace.h>
+
+#include "eal_windows.h"
+
+enum alarm_state {
+	ALARM_ARMED,
+	ALARM_TRIGGERED,
+	ALARM_CANCELLED
+};
+
+struct alarm_entry {
+	LIST_ENTRY(alarm_entry) next;
+	rte_eal_alarm_callback cb_fn;
+	void *cb_arg;
+	HANDLE timer;
+	atomic_uint state;
+};
+
+static LIST_HEAD(alarm_list, alarm_entry) alarm_list = LIST_HEAD_INITIALIZER();
+
+static rte_spinlock_t alarm_lock = RTE_SPINLOCK_INITIALIZER;
+
+static int intr_thread_exec(void (*func)(void *arg), void *arg);
+
+static void
+alarm_remove_unsafe(struct alarm_entry *ap)
+{
+	LIST_REMOVE(ap, next);
+	CloseHandle(ap->timer);
+	free(ap);
+}
+
+static void
+alarm_callback(void *arg, DWORD low __rte_unused, DWORD high __rte_unused)
+{
+	struct alarm_entry *ap = arg;
+	unsigned int state = ALARM_ARMED;
+
+	if (!atomic_compare_exchange_strong(
+			&ap->state, &state, ALARM_TRIGGERED))
+		return;
+
+	ap->cb_fn(ap->cb_arg);
+
+	rte_spinlock_lock(&alarm_lock);
+	alarm_remove_unsafe(ap);
+	rte_spinlock_unlock(&alarm_lock);
+}
+
+struct alarm_task {
+	struct alarm_entry *entry;
+	LARGE_INTEGER deadline;
+	int ret;
+};
+
+static void
+alarm_set(void *arg)
+{
+	struct alarm_task *task = arg;
+
+	BOOL ret = SetWaitableTimer(
+		task->entry->timer, &task->deadline,
+		0, alarm_callback, task->entry, FALSE);
+	task->ret = ret ? 0 : (-1);
+}
+
+int
+rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb_fn, void *cb_arg)
+{
+	struct alarm_entry *ap;
+	HANDLE timer;
+	FILETIME ft;
+	struct alarm_task task;
+	int ret;
+
+	/* Calculate deadline ASAP, unit of measure = 100ns. */
+	GetSystemTimePreciseAsFileTime(&ft);
+	task.deadline.LowPart = ft.dwLowDateTime;
+	task.deadline.HighPart = ft.dwHighDateTime;
+	task.deadline.QuadPart += 10 * us;
+
+	ap = calloc(1, sizeof(*ap));
+	if (ap == NULL) {
+		RTE_LOG(ERR, EAL, "Cannot allocate alarm entry\n");
+		ret = -ENOMEM;
+		goto exit;
+	}
+
+	timer = CreateWaitableTimer(NULL, FALSE, NULL);
+	if (timer == NULL) {
+		RTE_LOG_WIN32_ERR("CreateWaitableTimer()");
+		ret = -EINVAL;
+		goto fail;
+	}
+
+	ap->timer = timer;
+	ap->cb_fn = cb_fn;
+	ap->cb_arg = cb_arg;
+	task.entry = ap;
+
+	/* Waitable timer must be set in the same thread that will
+	 * do an alertable wait for the alarm to trigger, that is,
+	 * in the interrupt thread. Setting can fail, so do it synchronously.
+	 */
+	ret = intr_thread_exec(alarm_set, &task);
+	if (ret < 0) {
+		RTE_LOG(ERR, EAL, "Cannot setup alarm in interrupt thread\n");
+		goto fail;
+	}
+
+	ret = task.ret;
+	if (ret < 0)
+		goto fail;
+
+	rte_spinlock_lock(&alarm_lock);
+	LIST_INSERT_HEAD(&alarm_list, ap, next);
+	rte_spinlock_unlock(&alarm_lock);
+
+	goto exit;
+
+fail:
+	if (timer != NULL)
+		CloseHandle(timer);
+	if (ap != NULL)
+		free(ap);
+
+exit:
+	rte_eal_trace_alarm_set(us, cb_fn, cb_arg, ret);
+	return ret;
+}
+
+static bool
+alarm_matches(const struct alarm_entry *ap,
+	rte_eal_alarm_callback cb_fn, void *cb_arg)
+{
+	bool any_arg = cb_arg == (void *)(-1);
+	return (ap->cb_fn == cb_fn) && (any_arg || ap->cb_arg == cb_arg);
+}
+
+int
+rte_eal_alarm_cancel(rte_eal_alarm_callback cb_fn, void *cb_arg)
+{
+	struct alarm_entry *ap;
+	unsigned int state;
+	int removed;
+	bool executing;
+
+	removed = 0;
+	do {
+		executing = false;
+
+		rte_spinlock_lock(&alarm_lock);
+
+		LIST_FOREACH(ap, &alarm_list, next) {
+			if (!alarm_matches(ap, cb_fn, cb_arg))
+				continue;
+
+			state = ALARM_ARMED;
+			if (atomic_compare_exchange_strong(
+					&ap->state, &state, ALARM_CANCELLED)) {
+				alarm_remove_unsafe(ap);
+				removed++;
+			} else if (state == ALARM_TRIGGERED)
+				executing = true;
+		}
+
+		rte_spinlock_unlock(&alarm_lock);
+	} while (executing);
+
+	rte_eal_trace_alarm_cancel(cb_fn, cb_arg, removed);
+	return removed;
+}
+
+struct intr_task {
+	void (*func)(void *arg);
+	void *arg;
+	rte_spinlock_t lock; /* unlocked at task completion */
+};
+
+static void
+intr_thread_entry(void *arg)
+{
+	struct intr_task *task = arg;
+	task->func(task->arg);
+	rte_spinlock_unlock(&task->lock);
+}
+
+static int
+intr_thread_exec(void (*func)(void *arg), void *arg)
+{
+	struct intr_task task;
+	int ret;
+
+	task.func = func;
+	task.arg = arg;
+	rte_spinlock_init(&task.lock);
+
+	/* Make timers more precise by synchronizing in userspace. */
+	rte_spinlock_lock(&task.lock);
+	ret = eal_intr_thread_schedule(intr_thread_entry, &task);
+	if (ret < 0) {
+		RTE_LOG(ERR, EAL, "Cannot schedule task to interrupt thread\n");
+		return -EINVAL;
+	}
+
+	/* Wait for the task to complete. */
+	rte_spinlock_lock(&task.lock);
+	return 0;
+}
diff --git a/lib/librte_eal/windows/meson.build b/lib/librte_eal/windows/meson.build
index b690bc6b0..3b2faf29e 100644
--- a/lib/librte_eal/windows/meson.build
+++ b/lib/librte_eal/windows/meson.build
@@ -5,6 +5,7 @@ subdir('include')
 
 sources += files(
 	'eal.c',
+	'eal_alarm.c',
 	'eal_debug.c',
 	'eal_file.c',
 	'eal_hugepages.c',
-- 
2.25.4