fabricd: reimplement LSP transmission logic

Before this commit, isisd/fabricd maintained a bitfield for each LSP
to track the SRM bit for each circuit, which specifies whether an LSP
needs to be sent on that circuit. Every second, it would scan over all
LSPs in `lsp_tick` and queue them up for transmission accordingly.

This design has two drawbacks: a) it scales poorly b) it adds
unacceptable latency to the update process: each router takes a random
amount of time between 0 and 1 seconds to forward an update. In a
network with a diamter of 10, it might already take 10 seconds for an
update to traverse the network.

To mitigate this, a new design was chosen. Instead of tracking SRM in a
bitfield, have one tx_queue per circuit and declare that an LSP is in
that queue if and only if it would have SRM set for that circuit.

This way, we can track SRM similarly as we did before, however, on
insertion into the LSP queue, we can add a timer for (re)transmission,
alleviating the need for a periodic scan with LSP tick and reducing the
latency for forwarding of updates.

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

1 files changed, 3 insertions, 1 deletions

diff --git a/isisd/isis_pdu.h b/isisd/isis_pdu.h
index c69bfedea..ea19de259 100644
--- a/isisd/isis_pdu.h
+++ b/isisd/isis_pdu.h
@@ -24,6 +24,8 @@
 #ifndef _ZEBRA_ISIS_PDU_H
 #define _ZEBRA_ISIS_PDU_H
 
+#include "isisd/isis_tx_queue.h"
+
 #ifdef __SUNPRO_C
 #pragma pack(1)
 #endif
@@ -212,7 +214,7 @@ int send_l1_csnp(struct thread *thread);
 int send_l2_csnp(struct thread *thread);
 int send_l1_psnp(struct thread *thread);
 int send_l2_psnp(struct thread *thread);
-int send_lsp(struct thread *thread);
+void send_lsp(void *arg, struct isis_lsp *lsp, enum isis_tx_type tx_type);
 void fill_fixed_hdr(uint8_t pdu_type, struct stream *stream);
 int send_hello(struct isis_circuit *circuit, int level);
 int isis_handle_pdu(struct isis_circuit *circuit, uint8_t *ssnpa);