[ovs-dev] [PATCH 1/6] Make polling fds persistent
anton.ivanov at cambridgegreys.com
anton.ivanov at cambridgegreys.com
Mon Jul 6 08:20:09 UTC 2020
From: Anton Ivanov <anton.ivanov at cambridgegreys.com>
Saves on:
1. Allocation and disposal of a hash map per iteration in all threads
2. Re-population of the hashmap with all fds per iteration
3. Walking of the hashmap to construct a pollfd array per iteration
4. Allocating/deallocating the pollfd array per iteration
5. Decreases costs on various lookups
Compared to older attempts to do this, this emulates strictly the old
behaviour and is 100% backwards compatible with the old approach.
Unix only - the unix poll loop has been pulled to a new file.
Signed-off-by: Anton Ivanov <anton.ivanov at cambridgegreys.com>
---
lib/automake.mk | 3 +-
lib/poll-loop-unix.c | 415 +++++++++++++++++++++++++++++++++++++++++++
lib/poll-loop.c | 19 +-
3 files changed, 418 insertions(+), 19 deletions(-)
create mode 100644 lib/poll-loop-unix.c
diff --git a/lib/automake.mk b/lib/automake.mk
index 86940ccd2..39ff70650 100644
--- a/lib/automake.mk
+++ b/lib/automake.mk
@@ -242,7 +242,6 @@ lib_libopenvswitch_la_SOURCES = \
lib/perf-counter.c \
lib/stopwatch.h \
lib/stopwatch.c \
- lib/poll-loop.c \
lib/process.c \
lib/process.h \
lib/pvector.c \
@@ -349,6 +348,7 @@ lib_libopenvswitch_la_SOURCES += \
lib/route-table-stub.c \
lib/if-notifier-stub.c \
lib/stream-windows.c \
+ lib/poll-loop.c \
lib/strsep.c
else
lib_libopenvswitch_la_SOURCES += \
@@ -357,6 +357,7 @@ lib_libopenvswitch_la_SOURCES += \
lib/signals.c \
lib/signals.h \
lib/socket-util-unix.c \
+ lib/poll-loop-unix.c \
lib/stream-unix.c
endif
diff --git a/lib/poll-loop-unix.c b/lib/poll-loop-unix.c
new file mode 100644
index 000000000..0fb137855
--- /dev/null
+++ b/lib/poll-loop-unix.c
@@ -0,0 +1,415 @@
+/*
+ * Copyright (c) 2020 Red Hat Inc
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014 Nicira, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+#include "openvswitch/poll-loop.h"
+#include <errno.h>
+#include <inttypes.h>
+#include <poll.h>
+#include <stdlib.h>
+#include <string.h>
+#include "coverage.h"
+#include "openvswitch/dynamic-string.h"
+#include "fatal-signal.h"
+#include "openvswitch/list.h"
+#include "ovs-thread.h"
+#include "seq.h"
+#include "socket-util.h"
+#include "timeval.h"
+#include "openvswitch/vlog.h"
+#include "openvswitch/hmap.h"
+#include "hash.h"
+
+VLOG_DEFINE_THIS_MODULE(poll_loop);
+
+COVERAGE_DEFINE(poll_create_node);
+COVERAGE_DEFINE(poll_zero_timeout);
+
+#define POLLFD_INCREMENT 16;
+
+/* The poll_node structures are used solely as metadata for
+ * the pollfd array associated with the loop. That pollfd
+ * array is persistent and does not need to be regenerated
+ * on every iteration.
+ */
+
+struct poll_node {
+ struct hmap_node hmap_node;
+ int index; /* index in the pollfd array */
+ const char *where; /* Where poll_node was created. */
+};
+
+struct poll_loop {
+ /* All active poll waiters. */
+ struct hmap poll_nodes;
+
+ /* Time at which to wake up the next call to poll_block(), LLONG_MIN to
+ * wake up immediately, or LLONG_MAX to wait forever. */
+ long long int timeout_when; /* In msecs as returned by time_msec(). */
+ const char *timeout_where; /* Where 'timeout_when' was set. */
+ struct pollfd * watched; /* list of descriptors and event masks passed to poll */
+ int watched_size; /* size of the watched allocation */
+};
+
+static struct poll_loop *poll_loop(void);
+
+/* Look up the node with same fd or wevent. */
+static struct poll_node *
+find_poll_node(struct poll_loop *loop, int fd)
+{
+ struct poll_node *node;
+
+ HMAP_FOR_EACH_WITH_HASH (node, hmap_node,
+ hash_2words(fd, 0),
+ &loop->poll_nodes) {
+ if (fd && loop->watched[node->index].fd == fd) {
+ return node;
+ }
+ }
+ return NULL;
+}
+
+/* On Unix based systems:
+ *
+ * Registers 'fd' as waiting for the specified 'events' (which should be
+ * POLLIN or POLLOUT or POLLIN | POLLOUT). The following call to
+ * poll_block() will wake up when 'fd' becomes ready for one or more of the
+ * requested events. The 'fd's are given to poll() function later.
+ *
+ * The event registration is one-shot: only the following call to
+ * poll_block() is affected. The event will need to be re-registered after
+ * poll_block() is called if it is to persist.
+ *
+ * ('where' is used in debug logging. Commonly one would use poll_fd_wait() to
+ * automatically provide the caller's source file and line number for
+ * 'where'.) */
+
+
+static void
+poll_create_node(int fd, short int events, const char *where)
+{
+ struct poll_loop *loop = poll_loop();
+ struct poll_node *node;
+
+ COVERAGE_INC(poll_create_node);
+
+ /* Check for duplicate. If found, "or" the events. */
+ node = find_poll_node(loop, fd);
+ if (node) {
+ loop->watched[node->index].events |= events;
+ /* we overwrite the original where with the value for
+ * this invocation */
+ node->where = where;
+ } else {
+ node = xzalloc(sizeof *node);
+ hmap_insert(&loop->poll_nodes, &node->hmap_node,
+ hash_2words(fd, 0));
+
+ /* If the hash has grown bigger than its matching pollfd array
+ * allocation, allocate a new one and copy all elements there
+ */
+ if (hmap_count(&loop->poll_nodes) > loop->watched_size) {
+ struct pollfd *resized_watched;
+
+ loop->watched_size += POLLFD_INCREMENT;
+ resized_watched = xzalloc(sizeof(struct pollfd) * loop->watched_size);
+ memcpy(resized_watched, loop->watched, sizeof(struct pollfd) * (loop->watched_size - 1));
+ free(loop->watched);
+ loop->watched = resized_watched;
+ }
+ /* insert the new record at the end of the pollfd array */
+ node->index = hmap_count(&loop->poll_nodes) - 1;
+ loop->watched[node->index].fd = fd;
+ loop->watched[node->index].events = events | POLLHUP | POLLERR;
+ node->where = where;
+ }
+}
+
+/* Registers 'fd' as waiting for the specified 'events' (which should be POLLIN
+ * or POLLOUT or POLLIN | POLLOUT). The following call to poll_block() will
+ * wake up when 'fd' becomes ready for one or more of the requested events.
+ *
+ * The event registration is one-shot: only the following call to poll_block()
+ * is affected. The event will need to be re-registered after poll_block() is
+ * called if it is to persist.
+ *
+ * ('where' is used in debug logging. Commonly one would use poll_fd_wait() to
+ * automatically provide the caller's source file and line number for
+ * 'where'.) */
+void
+poll_fd_wait_at(int fd, short int events, const char *where)
+{
+ poll_create_node(fd, events, where);
+}
+
+/* Causes the following call to poll_block() to block for no more than 'msec'
+ * milliseconds. If 'msec' is nonpositive, the following call to poll_block()
+ * will not block at all.
+ *
+ * The timer registration is one-shot: only the following call to poll_block()
+ * is affected. The timer will need to be re-registered after poll_block() is
+ * called if it is to persist.
+ *
+ * ('where' is used in debug logging. Commonly one would use poll_timer_wait()
+ * to automatically provide the caller's source file and line number for
+ * 'where'.) */
+void
+poll_timer_wait_at(long long int msec, const char *where)
+{
+ long long int now = time_msec();
+ long long int when;
+
+ if (msec <= 0) {
+ /* Wake up immediately. */
+ when = LLONG_MIN;
+ } else if ((unsigned long long int) now + msec <= LLONG_MAX) {
+ /* Normal case. */
+ when = now + msec;
+ } else {
+ /* now + msec would overflow. */
+ when = LLONG_MAX;
+ }
+
+ poll_timer_wait_until_at(when, where);
+}
+
+/* Causes the following call to poll_block() to wake up when the current time,
+ * as returned by time_msec(), reaches 'when' or later. If 'when' is earlier
+ * than the current time, the following call to poll_block() will not block at
+ * all.
+ *
+ * The timer registration is one-shot: only the following call to poll_block()
+ * is affected. The timer will need to be re-registered after poll_block() is
+ * called if it is to persist.
+ *
+ * ('where' is used in debug logging. Commonly one would use
+ * poll_timer_wait_until() to automatically provide the caller's source file
+ * and line number for 'where'.) */
+void
+poll_timer_wait_until_at(long long int when, const char *where)
+{
+ struct poll_loop *loop = poll_loop();
+ if (when < loop->timeout_when) {
+ loop->timeout_when = when;
+ loop->timeout_where = where;
+ }
+}
+
+/* Causes the following call to poll_block() to wake up immediately, without
+ * blocking.
+ *
+ * ('where' is used in debug logging. Commonly one would use
+ * poll_immediate_wake() to automatically provide the caller's source file and
+ * line number for 'where'.) */
+void
+poll_immediate_wake_at(const char *where)
+{
+ poll_timer_wait_at(0, where);
+}
+
+/* Logs, if appropriate, that the poll loop was awakened by an event
+ * registered at 'where' (typically a source file and line number). The other
+ * arguments have two possible interpretations:
+ *
+ * - If 'pollfd' is nonnull then it should be the "struct pollfd" that caused
+ * the wakeup. 'timeout' is ignored.
+ *
+ * - If 'pollfd' is NULL then 'timeout' is the number of milliseconds after
+ * which the poll loop woke up.
+ */
+static void
+log_wakeup(const char *where, const struct pollfd *pollfd, int timeout)
+{
+ static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(10, 10);
+ enum vlog_level level;
+ int cpu_usage;
+ struct ds s;
+
+ cpu_usage = get_cpu_usage();
+ if (VLOG_IS_DBG_ENABLED()) {
+ level = VLL_DBG;
+ } else if (cpu_usage > 50
+ && !thread_is_pmd()
+ && !VLOG_DROP_INFO(&rl)) {
+ level = VLL_INFO;
+ } else {
+ return;
+ }
+
+ ds_init(&s);
+ ds_put_cstr(&s, "wakeup due to ");
+ if (pollfd) {
+ char *description = describe_fd(pollfd->fd);
+ if (pollfd->revents & POLLIN) {
+ ds_put_cstr(&s, "[POLLIN]");
+ }
+ if (pollfd->revents & POLLOUT) {
+ ds_put_cstr(&s, "[POLLOUT]");
+ }
+ if (pollfd->revents & POLLERR) {
+ ds_put_cstr(&s, "[POLLERR]");
+ }
+ if (pollfd->revents & POLLHUP) {
+ ds_put_cstr(&s, "[POLLHUP]");
+ }
+ if (pollfd->revents & POLLNVAL) {
+ ds_put_cstr(&s, "[POLLNVAL]");
+ }
+ ds_put_format(&s, " on fd %d (%s)", pollfd->fd, description);
+ free(description);
+ } else {
+ ds_put_format(&s, "%d-ms timeout", timeout);
+ }
+ if (where) {
+ ds_put_format(&s, " at %s", where);
+ }
+ if (cpu_usage >= 0) {
+ ds_put_format(&s, " (%d%% CPU usage)", cpu_usage);
+ }
+ VLOG(level, "%s", ds_cstr(&s));
+ ds_destroy(&s);
+}
+
+static void
+free_poll_nodes(struct poll_loop *loop)
+{
+ struct poll_node *node, *next;
+
+ HMAP_FOR_EACH_SAFE (node, next, hmap_node, &loop->poll_nodes) {
+ hmap_remove(&loop->poll_nodes, &node->hmap_node);
+ free(node);
+ }
+}
+
+/* Blocks until one or more of the events registered with poll_fd_wait()
+ * occurs, or until the minimum duration registered with poll_timer_wait()
+ * elapses, or not at all if poll_immediate_wake() has been called. */
+void
+poll_block(void)
+{
+ struct poll_loop *loop = poll_loop();
+ struct poll_node *node, *moved_node;
+ int elapsed;
+ int retval;
+ 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);
+ }
+
+ timewarp_run();
+
+ /* We do not need to pre-process the pollfd array in any way - it is
+ * ready for use.
+ */
+
+ retval = time_poll(loop->watched, hmap_count(&loop->poll_nodes), 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));
+ } else if (!retval) {
+ log_wakeup(loop->timeout_where, NULL, elapsed);
+ } else if (get_cpu_usage() > 50 || VLOG_IS_DBG_ENABLED()) {
+ for (i = 0; i < hmap_count(&loop->poll_nodes); i++) {
+ if (loop->watched[i].revents) {
+ node = find_poll_node(loop, loop->watched[i].fd);
+ ovs_assert(node != NULL);
+ log_wakeup(node->where, &loop->watched[i], 0);
+ }
+ }
+ }
+
+ /* Update the pollfd array to reproduce one-shot behaviour
+ * and reap any fds which have been closed in the meantime
+ */
+
+ i = 0;
+ while (i < hmap_count(&loop->poll_nodes)) {
+ node = find_poll_node(loop, loop->watched[i].fd);
+ ovs_assert(node != NULL);
+ if (loop->watched[i].revents & (POLLHUP | POLLNVAL)) {
+ /* FD was closed - reap */
+ if (i < (hmap_count(&loop->poll_nodes) - 1)) {
+ /* move last record to this index position */
+ moved_node = find_poll_node(
+ loop,
+ loop->watched[hmap_count(&loop->poll_nodes) - 1].fd);
+ ovs_assert(moved_node != NULL);
+ loop->watched[i] = loop->watched[hmap_count(&loop->poll_nodes) - 1];
+ moved_node->index = i;
+ }
+ hmap_remove(&loop->poll_nodes, &node->hmap_node);
+ /* note - we do not i++ here as we have not processed the node
+ * which we have moved from the tail of the array into the hole
+ */
+ } else {
+ /* Clear events to replicate one-shot behaviour. Leave file
+ * close related events intact so we can track file closures
+ */
+ loop->watched[i].events = (POLLHUP & POLLERR);
+ i++;
+ }
+ }
+
+ loop->timeout_when = LLONG_MAX;
+ loop->timeout_where = NULL;
+
+ /* Handle any pending signals before doing anything else. */
+ fatal_signal_run();
+
+ seq_woke();
+}
+
+static void
+free_poll_loop(void *loop_)
+{
+ struct poll_loop *loop = loop_;
+
+ free_poll_nodes(loop);
+ hmap_destroy(&loop->poll_nodes);
+ free(loop->watched);
+ free(loop);
+}
+
+static struct poll_loop *
+poll_loop(void)
+{
+ static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
+ static pthread_key_t key;
+ struct poll_loop *loop;
+
+ if (ovsthread_once_start(&once)) {
+ xpthread_key_create(&key, free_poll_loop);
+ ovsthread_once_done(&once);
+ }
+
+ loop = pthread_getspecific(key);
+ if (!loop) {
+ loop = xzalloc(sizeof *loop);
+ loop->timeout_when = LLONG_MAX;
+ hmap_init(&loop->poll_nodes);
+ loop->watched_size = POLLFD_INCREMENT;
+ loop->watched = xzalloc(sizeof(struct pollfd) * loop->watched_size);
+ xpthread_setspecific(key, loop);
+ }
+ return loop;
+}
diff --git a/lib/poll-loop.c b/lib/poll-loop.c
index 4e751ff2c..0eef47ae8 100644
--- a/lib/poll-loop.c
+++ b/lib/poll-loop.c
@@ -77,14 +77,7 @@ find_poll_node(struct poll_loop *loop, int fd, HANDLE wevent)
return NULL;
}
-/* On Unix based systems:
- *
- * Registers 'fd' as waiting for the specified 'events' (which should be
- * POLLIN or POLLOUT or POLLIN | POLLOUT). The following call to
- * poll_block() will wake up when 'fd' becomes ready for one or more of the
- * requested events. The 'fd's are given to poll() function later.
- *
- * On Windows system:
+/* On Windows system:
*
* If 'fd' is specified, create a new 'wevent'. Association of 'fd' and
* 'wevent' for 'events' happens in poll_block(). If 'wevent' is specified,
@@ -120,11 +113,9 @@ poll_create_node(int fd, HANDLE wevent, short int events, const char *where)
hash_2words(fd, (uint32_t)wevent));
node->pollfd.fd = fd;
node->pollfd.events = events;
-#ifdef _WIN32
if (!wevent) {
wevent = CreateEvent(NULL, FALSE, FALSE, NULL);
}
-#endif
node->wevent = wevent;
node->where = where;
}
@@ -149,7 +140,6 @@ poll_fd_wait_at(int fd, short int events, const char *where)
poll_create_node(fd, 0, events, where);
}
-#ifdef _WIN32
/* Registers for the next call to poll_block() to wake up when 'wevent' is
* signaled.
*
@@ -165,7 +155,6 @@ poll_wevent_wait_at(HANDLE wevent, const char *where)
{
poll_create_node(0, wevent, 0, where);
}
-#endif /* _WIN32 */
/* Causes the following call to poll_block() to block for no more than 'msec'
* milliseconds. If 'msec' is nonpositive, the following call to poll_block()
@@ -302,12 +291,10 @@ free_poll_nodes(struct poll_loop *loop)
HMAP_FOR_EACH_SAFE (node, next, hmap_node, &loop->poll_nodes) {
hmap_remove(&loop->poll_nodes, &node->hmap_node);
-#ifdef _WIN32
if (node->wevent && node->pollfd.fd) {
WSAEventSelect(node->pollfd.fd, NULL, 0);
CloseHandle(node->wevent);
}
-#endif
free(node);
}
}
@@ -337,15 +324,12 @@ poll_block(void)
timewarp_run();
pollfds = xmalloc(hmap_count(&loop->poll_nodes) * sizeof *pollfds);
-#ifdef _WIN32
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;
-#ifdef _WIN32
wevents[i] = node->wevent;
if (node->pollfd.fd && node->wevent) {
short int wsa_events = 0;
@@ -357,7 +341,6 @@ poll_block(void)
}
WSAEventSelect(node->pollfd.fd, node->wevent, wsa_events);
}
-#endif
i++;
}
--
2.20.1
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