Rate-limit scheduling of work-events

In general, events are code handling some some condition, which is
scheduled when such condition happened and executed independently from
I/O loop. Work-events are a subgroup of events that are scheduled
repeatedly until some (often significant) work is done (e.g. feeding
routes to protocol). All scheduled events are executed during each
I/O loop iteration.

Separate work-events from regular events to a separate queue and
rate limit their execution to a fixed number per I/O loop iteration.
That should prevent excess latency when many work-events are
scheduled at one time (e.g. simultaneous reload of many BGP sessions).
This commit is contained in:
Ondrej Zajicek (work) 2021-03-12 15:35:56 +01:00
parent 9cf3d53311
commit 7be3af7fa6
4 changed files with 66 additions and 6 deletions

View file

@ -23,6 +23,7 @@
#include "lib/event.h"
event_list global_event_list;
event_list global_work_list;
inline void
ev_postpone(event *e)
@ -114,6 +115,22 @@ ev_schedule(event *e)
ev_enqueue(&global_event_list, e);
}
/**
* ev_schedule_work - schedule a work-event.
* @e: an event
*
* This function schedules an event by enqueueing it to a system-wide work-event
* list which is run by the platform dependent code whenever appropriate. This
* is designated for work-events instead of regular events. They are executed
* less often in order to not clog I/O loop.
*/
void
ev_schedule_work(event *e)
{
if (!ev_active(e))
add_tail(&global_work_list, &e->n);
}
void io_log_event(void *hook, void *data);
/**
@ -136,10 +153,47 @@ ev_run_list(event_list *l)
event *e = SKIP_BACK(event, n, n);
/* This is ugly hack, we want to log just events executed from the main I/O loop */
if (l == &global_event_list)
if ((l == &global_event_list) || (l == &global_work_list))
io_log_event(e->hook, e->data);
ev_run(e);
}
return !EMPTY_LIST(*l);
}
int
ev_run_list_limited(event_list *l, uint limit)
{
node *n;
list tmp_list;
init_list(&tmp_list);
add_tail_list(&tmp_list, l);
init_list(l);
WALK_LIST_FIRST(n, tmp_list)
{
event *e = SKIP_BACK(event, n, n);
if (!limit)
break;
/* This is ugly hack, we want to log just events executed from the main I/O loop */
if ((l == &global_event_list) || (l == &global_work_list))
io_log_event(e->hook, e->data);
ev_run(e);
limit--;
}
if (!EMPTY_LIST(tmp_list))
{
/* Attach new items after the unprocessed old items */
add_tail_list(&tmp_list, l);
init_list(l);
add_tail_list(l, &tmp_list);
}
return !EMPTY_LIST(*l);
}

View file

@ -21,14 +21,17 @@ typedef struct event {
typedef list event_list;
extern event_list global_event_list;
extern event_list global_work_list;
event *ev_new(pool *);
void ev_run(event *);
#define ev_init_list(el) init_list(el)
void ev_enqueue(event_list *, event *);
void ev_schedule(event *);
void ev_schedule_work(event *);
void ev_postpone(event *);
int ev_run_list(event_list *);
int ev_run_list_limited(event_list *, uint);
static inline int
ev_active(event *e)

View file

@ -252,7 +252,7 @@ channel_schedule_feed(struct channel *c, int initial)
c->export_state = ES_FEEDING;
c->refeeding = !initial;
ev_schedule(c->feed_event);
ev_schedule_work(c->feed_event);
}
static void
@ -275,7 +275,7 @@ channel_feed_loop(void *ptr)
// DBG("Feeding protocol %s continued\n", p->name);
if (!rt_feed_channel(c))
{
ev_schedule(c->feed_event);
ev_schedule_work(c->feed_event);
return;
}
@ -291,7 +291,7 @@ channel_feed_loop(void *ptr)
/* Continue in feed - it will process routing table again from beginning */
c->refeed_count = 0;
ev_schedule(c->feed_event);
ev_schedule_work(c->feed_event);
return;
}
@ -471,7 +471,7 @@ channel_schedule_reload(struct channel *c)
ASSERT(c->channel_state == CS_UP);
rt_reload_channel_abort(c);
ev_schedule(c->reload_event);
ev_schedule_work(c->reload_event);
}
static void
@ -485,7 +485,7 @@ channel_reload_loop(void *ptr)
if (!rt_reload_channel(c))
{
ev_schedule(c->reload_event);
ev_schedule_work(c->reload_event);
return;
}

View file

@ -2161,6 +2161,7 @@ io_init(void)
{
init_list(&sock_list);
init_list(&global_event_list);
init_list(&global_work_list);
krt_io_init();
// XXX init_times();
// XXX update_times();
@ -2172,6 +2173,7 @@ io_init(void)
static int short_loops = 0;
#define SHORT_LOOP_MAX 10
#define WORK_EVENTS_MAX 10
void
io_loop(void)
@ -2189,6 +2191,7 @@ io_loop(void)
{
times_update(&main_timeloop);
events = ev_run_list(&global_event_list);
events = ev_run_list_limited(&global_work_list, WORK_EVENTS_MAX) || events;
timers_fire(&main_timeloop);
io_close_event();