From 8ceca1e18a46e8f20c9f0c0bf69dd140e0ff6773 Mon Sep 17 00:00:00 2001
From: Michal Sojka <sojkam1@fel.cvut.cz>
Date: Sun, 12 Jan 2014 23:47:34 +0100
Subject: [PATCH] Implement busy_poll (aka low latency) for read method

---
 ugw/ugw.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/ugw/ugw.c b/ugw/ugw.c
index 64d00b0..9458e7d 100644
--- a/ugw/ugw.c
+++ b/ugw/ugw.c
@@ -21,6 +21,10 @@
 #include <sys/mman.h>
 #include <arpa/inet.h>
 
+#ifndef SO_BUSY_POLL
+#define SO_BUSY_POLL 46
+#endif
+
 #define FRAME_SIZE 256
 #define BLOCK_SIZE 4096
 #define BLOCK_NR 2
@@ -36,6 +40,7 @@ char *devout = "can1";
 enum { IN_READ, IN_RECVMMSG, IN_MMAP, IN_MMAPBUSY } in_method = IN_READ;
 enum { WRITE, OUT_MMAP } out_method = WRITE;
 bool quiet = false;
+int busy_poll_us = 0;
 
 enum in2out {
 	STORE_ONLY,
@@ -80,6 +85,11 @@ void init_read(struct in_ctx *ctx)
 
 	s = CHECK(socket(PF_CAN, SOCK_RAW, CAN_RAW));
 
+	if (busy_poll_us) {
+		CHECK(setsockopt(s, SOL_SOCKET, SO_BUSY_POLL,
+				 &busy_poll_us, sizeof(busy_poll_us)));
+	}
+
 	strncpy(ifr.ifr_name, devin, sizeof(ifr.ifr_name));
 	if (-1 == ioctl(s, SIOCGIFINDEX, &ifr)) {
 		perror(devin);
@@ -313,8 +323,11 @@ int main(int argc, char *argv[])
 {
 	int opt;
 
-	while ((opt = getopt(argc, argv, "qr:t:")) != -1) {
+	while ((opt = getopt(argc, argv, "b:qr:t:")) != -1) {
 		switch (opt) {
+		case 'b':
+			busy_poll_us = atoi(optarg);
+			break;
 		case 'q':
 			quiet = true;
 			break;
-- 
2.39.2