[ovs-dev] [PATCH v5 1/2] Optimize the poll loop for poll_immediate_wake()
anton.ivanov at cambridgegreys.com
anton.ivanov at cambridgegreys.com
Wed Aug 4 08:34:18 UTC 2021
From: Anton Ivanov <anton.ivanov at cambridgegreys.com>
If we are not obtaining any useful information out of the poll(),
such as is a fd busy or not, we do not need to do a poll() if
an immediate_wake() has been requested.
This cuts out all the pollfd hash additions, forming the poll
arguments and the actual poll() after a call to
poll_immediate_wake()
Signed-off-by: Anton Ivanov <anton.ivanov at cambridgegreys.com>
---
lib/poll-loop.c | 82 +++++++++++++++++++++++++++++++++----------------
lib/timeval.c | 15 +++++++--
2 files changed, 68 insertions(+), 29 deletions(-)
diff --git a/lib/poll-loop.c b/lib/poll-loop.c
index 4e751ff2c..ce681129c 100644
--- a/lib/poll-loop.c
+++ b/lib/poll-loop.c
@@ -107,6 +107,13 @@ poll_create_node(int fd, HANDLE wevent, short int events, const char *where)
COVERAGE_INC(poll_create_node);
+ if (loop->timeout_when == LLONG_MIN) {
+ /* There was a previous request to bail out of this poll loop.
+ * There is no point to engage in yack shaving a poll hmap.
+ */
+ return;
+ }
+
/* Both 'fd' and 'wevent' cannot be set. */
ovs_assert(!fd != !wevent);
@@ -181,8 +188,21 @@ poll_wevent_wait_at(HANDLE wevent, const char *where)
void
poll_timer_wait_at(long long int msec, const char *where)
{
- long long int now = time_msec();
+ long long int now;
long long int when;
+ struct poll_loop *loop = poll_loop();
+
+ /* We have an outstanding request for an immediate wake -
+ * either explicit (from poll_immediate_wake()) or as a
+ * result of a previous timeout calculation which gave
+ * a negative timeout.
+ * No point trying to recalculate the timeout.
+ */
+ if (loop->timeout_when == LLONG_MIN) {
+ return;
+ }
+
+ now = time_msec();
if (msec <= 0) {
/* Wake up immediately. */
@@ -229,7 +249,7 @@ poll_timer_wait_until_at(long long int when, const char *where)
void
poll_immediate_wake_at(const char *where)
{
- poll_timer_wait_at(0, where);
+ poll_timer_wait_at(LLONG_MIN, where);
}
/* Logs, if appropriate, that the poll loop was awakened by an event
@@ -320,49 +340,57 @@ poll_block(void)
{
struct poll_loop *loop = poll_loop();
struct poll_node *node;
- struct pollfd *pollfds;
+ struct pollfd *pollfds = NULL;
HANDLE *wevents = NULL;
int elapsed;
- int retval;
+ int retval = 0;
int i;
- /* Register fatal signal events before actually doing any real work for
- * poll_block. */
- fatal_signal_wait();
if (loop->timeout_when == LLONG_MIN) {
COVERAGE_INC(poll_zero_timeout);
+ } else {
+ /* Register fatal signal poll events only if we intend to do real
+ * work for poll_block. The fatal signals themselves are handled
+ * in either case by invoking fatal_signal_run() at the end of the
+ * loop.
+ */
+ fatal_signal_wait();
}
timewarp_run();
- pollfds = xmalloc(hmap_count(&loop->poll_nodes) * sizeof *pollfds);
+ if (loop->timeout_when != LLONG_MIN) {
+ pollfds = xmalloc(hmap_count(&loop->poll_nodes) * sizeof *pollfds);
#ifdef _WIN32
- wevents = xmalloc(hmap_count(&loop->poll_nodes) * sizeof *wevents);
+ wevents = xmalloc(hmap_count(&loop->poll_nodes) * sizeof *wevents);
#endif
- /* Populate with all the fds and events. */
- i = 0;
- HMAP_FOR_EACH (node, hmap_node, &loop->poll_nodes) {
- pollfds[i] = node->pollfd;
+ /* Populate with all the fds and events. */
+ i = 0;
+ HMAP_FOR_EACH (node, hmap_node, &loop->poll_nodes) {
+ pollfds[i] = node->pollfd;
#ifdef _WIN32
- wevents[i] = node->wevent;
- if (node->pollfd.fd && node->wevent) {
- short int wsa_events = 0;
- if (node->pollfd.events & POLLIN) {
- wsa_events |= FD_READ | FD_ACCEPT | FD_CLOSE;
+ wevents[i] = node->wevent;
+ if (node->pollfd.fd && node->wevent) {
+ short int wsa_events = 0;
+ if (node->pollfd.events & POLLIN) {
+ wsa_events |= FD_READ | FD_ACCEPT | FD_CLOSE;
+ }
+ if (node->pollfd.events & POLLOUT) {
+ wsa_events |= FD_WRITE | FD_CONNECT | FD_CLOSE;
+ }
+ WSAEventSelect(node->pollfd.fd, node->wevent, wsa_events);
}
- if (node->pollfd.events & POLLOUT) {
- wsa_events |= FD_WRITE | FD_CONNECT | FD_CLOSE;
- }
- WSAEventSelect(node->pollfd.fd, node->wevent, wsa_events);
- }
#endif
- i++;
- }
+ i++;
+ }
- retval = time_poll(pollfds, hmap_count(&loop->poll_nodes), wevents,
- loop->timeout_when, &elapsed);
+ retval = time_poll(pollfds, hmap_count(&loop->poll_nodes), wevents,
+ loop->timeout_when, &elapsed);
+ } else {
+ retval = time_poll(NULL, 0, NULL, loop->timeout_when, &elapsed);
+ }
if (retval < 0) {
static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
VLOG_ERR_RL(&rl, "poll: %s", ovs_strerror(-retval));
diff --git a/lib/timeval.c b/lib/timeval.c
index 193c7bab1..dbfbcb9e6 100644
--- a/lib/timeval.c
+++ b/lib/timeval.c
@@ -305,6 +305,7 @@ time_poll(struct pollfd *pollfds, int n_pollfds, HANDLE *handles OVS_UNUSED,
for (;;) {
long long int now = time_msec();
int time_left;
+ retval = 0;
if (now >= timeout_when) {
time_left = 0;
@@ -323,14 +324,24 @@ time_poll(struct pollfd *pollfds, int n_pollfds, HANDLE *handles OVS_UNUSED,
}
#ifndef _WIN32
- retval = poll(pollfds, n_pollfds, time_left);
+ /* If timeout_when is LLONG_MIN, we should skip the poll().
+ * We do not skip on time_left == 0, because we may have
+ * ended up with time_left = 0 after a poll with valid
+ * pollfds was interrupted and restarted.
+ */
+ if (timeout_when != LLONG_MIN) {
+ retval = poll(pollfds, n_pollfds, time_left);
+ }
if (retval < 0) {
retval = -errno;
}
#else
if (n_pollfds > MAXIMUM_WAIT_OBJECTS) {
VLOG_ERR("Cannot handle more than maximum wait objects\n");
- } else if (n_pollfds != 0) {
+ } else if (n_pollfds != 0 && timeout_when != LLONG_MIN) {
+ /* If there is a request for an immediate_wake, timeout_when
+ * is LLONG_MIN. In this case we skip the actual call.
+ */
retval = WaitForMultipleObjects(n_pollfds, handles, FALSE,
time_left);
}
--
2.20.1
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