KRT: Scan routing tables separetely on linux to avoid congestion

Remove compile-time sysdep option CONFIG_ALL_TABLES_AT_ONCE, replace it
with runtime ability to run either separate table scans or shared scan.

On Linux, use separate table scans by default when the netlink socket
option NETLINK_GET_STRICT_CHK is available, but retreat to shared scan
when it fails.

Running separate table scans has advantages where some routing tables are
managed independently, e.g. when multiple routing daemons are running on
the same machine, as kernel routing table modification performance is
significantly reduced when the table is modified while it is being
scanned.

Thanks Daniel Gröber for the original patch and Toke Høiland-Jørgensen
for suggestions.

1 files changed, 40 insertions, 32 deletions

diff --git a/sysdep/unix/krt.c b/sysdep/unix/krt.c
index a02cf977..342adee5 100644
--- a/sysdep/unix/krt.c
+++ b/sysdep/unix/krt.c
@@ -783,18 +783,17 @@ krt_got_route_async(struct krt_proto *p, rte *e, int new)
   rte_free(e);
 }
 
+
 /*
  *	Periodic scanning
  */
 
-
-#ifdef CONFIG_ALL_TABLES_AT_ONCE
-
-static timer *krt_scan_timer;
-static int krt_scan_count;
+static timer *krt_scan_all_timer;
+static int krt_scan_all_count;
+static _Bool krt_scan_all_tables;
 
 static void
-krt_scan(timer *t UNUSED)
+krt_scan_all(timer *t UNUSED)
 {
   struct krt_proto *p;
   node *n;
@@ -815,35 +814,42 @@ krt_scan(timer *t UNUSED)
 }
 
 static void
-krt_scan_timer_start(struct krt_proto *p)
+krt_scan_all_timer_start(struct krt_proto *p)
 {
-  if (!krt_scan_count)
-    krt_scan_timer = tm_new_init(krt_pool, krt_scan, NULL, KRT_CF->scan_time, 0);
+  if (!krt_scan_all_count)
+    krt_scan_all_timer = tm_new_init(krt_pool, krt_scan_all, NULL, KRT_CF->scan_time, 0);
 
-  krt_scan_count++;
+  krt_scan_all_count++;
 
-  tm_start(krt_scan_timer, 1 S);
+  tm_start(krt_scan_all_timer, 1 S);
 }
 
 static void
-krt_scan_timer_stop(struct krt_proto *p UNUSED)
+krt_scan_all_timer_stop(void)
 {
-  krt_scan_count--;
+  ASSERT(krt_scan_all_count > 0);
+
+  krt_scan_all_count--;
 
-  if (!krt_scan_count)
+  if (!krt_scan_all_count)
   {
-    rfree(krt_scan_timer);
-    krt_scan_timer = NULL;
+    rfree(krt_scan_all_timer);
+    krt_scan_all_timer = NULL;
   }
 }
 
 static void
-krt_scan_timer_kick(struct krt_proto *p UNUSED)
+krt_scan_all_timer_kick(void)
 {
-  tm_start(krt_scan_timer, 0);
+  tm_start(krt_scan_all_timer, 0);
+}
+
+void
+krt_use_shared_scan(void)
+{
+  krt_scan_all_tables = 1;
 }
 
-#else
 
 static void
 krt_scan(timer *t)
@@ -861,26 +867,33 @@ krt_scan(timer *t)
 static void
 krt_scan_timer_start(struct krt_proto *p)
 {
-  p->scan_timer = tm_new_init(p->p.pool, krt_scan, p, KRT_CF->scan_time, 0);
-  tm_start(p->scan_timer, 1 S);
+  if (krt_scan_all_tables)
+    krt_scan_all_timer_start(p);
+  else
+  {
+    p->scan_timer = tm_new_init(p->p.pool, krt_scan, p, KRT_CF->scan_time, 0);
+    tm_start(p->scan_timer, 1 S);
+  }
 }
 
 static void
 krt_scan_timer_stop(struct krt_proto *p)
 {
-  tm_stop(p->scan_timer);
+  if (krt_scan_all_tables)
+    krt_scan_all_timer_stop();
+  else
+    tm_stop(p->scan_timer);
 }
 
 static void
 krt_scan_timer_kick(struct krt_proto *p)
 {
-  tm_start(p->scan_timer, 0);
+  if (krt_scan_all_tables)
+    krt_scan_all_timer_kick();
+  else
+    tm_start(p->scan_timer, 0);
 }
 
-#endif
-
-
-
 
 /*
  *	Updates
@@ -1016,11 +1029,6 @@ krt_postconfig(struct proto_config *CF)
   if (! proto_cf_main_channel(CF))
     cf_error("Channel not specified");
 
-#ifdef CONFIG_ALL_TABLES_AT_ONCE
-  if (krt_cf->scan_time != cf->scan_time)
-    cf_error("All kernel syncers must use the same table scan interval");
-#endif
-
   struct channel_config *cc = proto_cf_main_channel(CF);
   struct rtable_config *tab = cc->table;
   if (tab->krt_attached)