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Subject[PATCH]: Make UDP wait for 64k of free buffer before telling select/poll there is space to send.
This should allow better handling of large (> 2048 byte) UDP packets
when the socket write buffer is relatively large....

diff -u -r -N -X /home/greear/exclude.list linux/include/net/sock.h
--- linux/include/net/sock.h Fri Dec 21 10:42:04 2001
+++ Sun Dec 23 12:22:52 2001
@@ -1230,7 +1230,16 @@
static inline int sock_writeable(struct sock *sk)
return sock_wspace(sk) >= SOCK_MIN_WRITE_SPACE;
+ /* The goal is to only signal writable when there is at least 64k of buffer space
+ * when your send buffers are 128k or bigger. The reason is that otherwise
+ * you get many failed UDP sends when you run > SOCK_MIN_WRITE_SPACE sized packets
+ * at extreme speed (ie faster than your network can keep up). This change is
+ * designed to make select/poll wait untill you can actually be assured of sending
+ * the UDP packet at least into the kernel buffers w/out dropping it.
+ * This puts us more in line with sock_dev_write_space in core/sock.c too. --Ben
+ */
+ return sock_wspace(sk) >= max(SOCK_MIN_WRITE_SPACE,
+ min((unsigned int)(0xFFFF), sk->sndbuf >> 1));

static inline int gfp_any(void)
Ben Greear <> <Ben_Greear AT>
President of Candela Technologies Inc

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