On 03/08/2021 00:29, Gaëtan Rivet wrote:
On Tue, Jul 20, 2021, at 17:06, [email protected] wrote:From: Anton Ivanov <[email protected]>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 <[email protected]>Hi Anton, Patch generally looks good to me. A few nits below.--- lib/poll-loop.c | 80 ++++++++++++++++++++++++++++++++----------------- lib/timeval.c | 13 +++++++- 2 files changed, 65 insertions(+), 28 deletions(-) diff --git a/lib/poll-loop.c b/lib/poll-loop.c index 4e751ff2c..9452f6e22 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 +340,55 @@ 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 events only if we intend to do real work for + * poll_block. + */ + fatal_signal_wait();When should we avoid registering fatal signal events? Even for immediate wake, time_poll() will execute for general upkeep (coverage + RCU), should a fatal signal handler not be installed in that case?
The fatal signal events are handled in ALL cases in the fatal_signal_run() which is towards the end of the poll loop. fatal_singal_wait only adds the pipe to the fds. If we are not polling on that fd anyway, no point adding it either.
}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..ef09a15e0 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; @@ -323,7 +324,14 @@ 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) {The _WIN32 case checks 'n_pollfds != 0' before calling. Should both be aligned? Maybe the _WIN32 should avoid the call if 'n_pollfds == 0 || timeout_when == LLONG_MIN'?
Sure. I try to avoid touching the WIN32 code as I do not have an environment to test it.
+ retval = poll(pollfds, n_pollfds, time_left); + } if (retval < 0) { retval = -errno; } @@ -331,6 +339,9 @@ time_poll(struct pollfd *pollfds, int n_pollfds, HANDLE *handles OVS_UNUSED, if (n_pollfds > MAXIMUM_WAIT_OBJECTS) { VLOG_ERR("Cannot handle more than maximum wait objects\n"); } else if (n_pollfds != 0) { + /* If we are doing an immediate_wake shortcut n_pollfds is + * zero, so we skip the actual call. + */I find this sentence hard to read. I would suggest instead: /* n_pollfds can be zero on immediate_wake. * In that case the call is not necessary. */retval = WaitForMultipleObjects(n_pollfds, handles, FALSE, time_left); } -- 2.20.1 _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
-- Anton R. Ivanov Cambridgegreys Limited. Registered in England. Company Number 10273661 https://www.cambridgegreys.com/ _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
