isisd: delay lsp regeneration while events are still coming in

When there is a stream of events coming in, where IS-IS learns
about a lot of updates, IS-IS would regenerate its LSPs before
the updates have been processed completely.

This causes suboptimal convergence because the intermediate state
will be flooded. Only after the configured `lsp_gen_interval`, a
new update with the correct and final state will be generated.

Resolve this by holding off LSP generation while there are still
events coming in.

Signed-off-by: Christian Franke <chris@opensourcerouting.org>

isisd/isis_lsp.c

@@ -1361,15 +1361,24 @@ static int lsp_refresh(struct thread *thread)
 	if ((area->is_type & level) == 0)
 		return ISIS_ERROR;
 
+	if (monotime_since(&area->last_lsp_refresh_event[level - 1], NULL) < 50000L) {
+		sched_debug("ISIS (%s): Still unstable, postpone LSP L%d refresh",
+			    area->area_tag, level);
+		_lsp_regenerate_schedule(area, level, 0, false,
+					 __func__, __FILE__, __LINE__);
+		return 0;
+	}
+
 	sched_debug(
 		"ISIS (%s): LSP L%d refresh timer expired. Refreshing LSP...",
 		area->area_tag, level);
 	return lsp_regenerate(area, level);
 }
 
 int _lsp_regenerate_schedule(struct isis_area *area, int level,
-			     int all_pseudo, const char *func,
-			     const char *file, int line)
+			     int all_pseudo, bool postpone,
+			     const char *func, const char *file,
+			     int line)
 {
 	struct isis_lsp *lsp;
 	uint8_t id[ISIS_SYS_ID_LEN + 2];
@@ -1397,6 +1406,10 @@ int _lsp_regenerate_schedule(struct isis_area *area, int level,
 		if (!((level & lvl) && (area->is_type & lvl)))
 			continue;
 
+		if (postpone) {
+			monotime(&area->last_lsp_refresh_event[lvl - 1]);
+		}
+
 		sched_debug(
 			"ISIS (%s): Checking whether L%d needs to be scheduled",
 			area->area_tag, lvl);

isisd/isis_lsp.h

@@ -55,11 +55,11 @@ int lsp_tick(struct thread *thread);
 
 int lsp_generate(struct isis_area *area, int level);
 #define lsp_regenerate_schedule(area, level, all_pseudo) \
-	_lsp_regenerate_schedule((area), (level), (all_pseudo), \
+	_lsp_regenerate_schedule((area), (level), (all_pseudo), true, \
 				 __func__, __FILE__, __LINE__)
 int _lsp_regenerate_schedule(struct isis_area *area, int level,
-			     int all_pseudo, const char *func,
-				     const char *file, int line);
+			     int all_pseudo, bool postpone,
+			     const char *func, const char *file, int line);
 int lsp_generate_pseudo(struct isis_circuit *circuit, int level);
 int lsp_regenerate_schedule_pseudo(struct isis_circuit *circuit, int level);
 

isisd/isisd.h

@@ -105,6 +105,7 @@ struct isis_area {
 	struct flags flags;
 	struct thread *t_tick; /* LSP walker */
 	struct thread *t_lsp_refresh[ISIS_LEVELS];
+	struct timeval last_lsp_refresh_event[ISIS_LEVELS];
 	/* t_lsp_refresh is used in two ways:
 	 * a) regular refresh of LSPs
 	 * b) (possibly throttled) updates to LSPs