[patch] 2.4.9 new socket option TCP_DELACK (RFC)

[Nivedita Singhvi <nivedita@xxxxxxxxxxx>]

This patch adds a new socket option TCP_DELACK, which 
disables the sending of delayed acks altogether on
that socket connection. Built against 2.4.9.

This was to test with and play with, more than anything
else, but figured others might be interested. Possibly 
useful in improving performance in the small packet and 
highly interactive app environment.

Arguments to include it in the source tree:

- possibly better performance in certain environments
- _very_ convenient for academic, benchmarking, and certain
  other environments to use 
- portability: its available on some other OS's, and
  so some apps that make use of it might want to continue
  to use it on Linux when ported here..
- makes the tcp engine more configurable based on what the
  user wants to do, and the easier it is to fiddle with things, 
  the more learning, innovation that happens on the OS, and 
  I'd like to encourage that happening on Linux ;)
- somewhat the same rationale behind allowing the users to
  to disable delayed sends (TCP_NODELAY) 

Cons:

- feature bloat (but its small, minimized diffs)
- makes the tcp engine more configurable based on what the
  user wants to do, but the user needs to know what they're 
  doing, given extra ack load (but ditto with other options, really)


I'd be interested in hearing if others found it useful,
or have any comments or feedback..

thanks,
Nivedita

-----
diff -urN linux-2.4.9/include/linux/tcp.h linux-2.4.9-da2/include/linux/tcp.h
--- linux-2.4.9/include/linux/tcp.h     Wed Aug 15 14:21:32 2001
+++ linux-2.4.9-da2/include/linux/tcp.h Sat Aug 25 10:44:01 2001
@@ -127,6 +127,7 @@
 #define TCP_WINDOW_CLAMP       10      /* Bound advertised window */
 #define TCP_INFO               11      /* Information about this connection. */
 #define TCP_QUICKACK           12      /* Block/reenable quick acks */
+#define TCP_NODELACK           13      /* Disable delayed acks */
 
 #define TCPI_OPT_TIMESTAMPS    1
 #define TCPI_OPT_SACK          2
diff -urN linux-2.4.9/include/net/sock.h linux-2.4.9-da2/include/net/sock.h
--- linux-2.4.9/include/net/sock.h      Wed Aug 15 14:21:32 2001
+++ linux-2.4.9-da2/include/net/sock.h  Sat Aug 25 10:44:01 2001
@@ -278,6 +278,7 @@
                __u32   lrcvtime;       /* timestamp of last received data 
packet*/
                __u16   last_seg_size;  /* Size of last incoming segment        
*/
                __u16   rcv_mss;        /* MSS used for delayed ACK decisions   
*/ 
+               __u8    no_delack;      /* no delayed acks at all */
        } ack;
 
        /* Data for direct copy to user */
diff -urN linux-2.4.9/net/ipv4/tcp.c linux-2.4.9-da2/net/ipv4/tcp.c
--- linux-2.4.9/net/ipv4/tcp.c  Wed Aug 15 01:22:17 2001
+++ linux-2.4.9-da2/net/ipv4/tcp.c      Sat Aug 25 11:11:48 2001
@@ -2305,6 +2305,10 @@
                }
                break;
 
+       case TCP_NODELACK:
+               tp->ack.no_delack = val > 0; 
+               break;
+       
        default:
                err = -ENOPROTOOPT;
                break;
@@ -2431,6 +2435,10 @@
        case TCP_QUICKACK:
                val = !tp->ack.pingpong;
                break;
+       case TCP_NODELACK:
+               val = tp->ack.no_delack;
+               break;
+
        default:
                return -ENOPROTOOPT;
        };
diff -urN linux-2.4.9/net/ipv4/tcp_input.c linux-2.4.9-da2/net/ipv4/tcp_input.c
--- linux-2.4.9/net/ipv4/tcp_input.c    Wed Aug 15 01:22:17 2001
+++ linux-2.4.9-da2/net/ipv4/tcp_input.c        Sat Aug 25 10:44:01 2001
@@ -3015,7 +3015,8 @@
        struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
 
            /* More than one full frame received... */
-       if (((tp->rcv_nxt - tp->rcv_wup) > tp->ack.rcv_mss
+       if (tp->ack.no_delack ||
+           ((tp->rcv_nxt - tp->rcv_wup) > tp->ack.rcv_mss
             /* ... and right edge of window advances far enough.
              * (tcp_recvmsg() will send ACK otherwise). Or...
              */
@@ -3351,7 +3352,8 @@
                        }
 
                        if (eaten) {
-                               if (tcp_in_quickack_mode(tp)) {
+                               if (tp->ack.no_delack ||
+                                   tcp_in_quickack_mode(tp)) {
                                        tcp_send_ack(sk);
                                } else {
                                        tcp_send_delayed_ack(sk);