net: tcp: add mib counters to track zero window transitions

Three counters are added:
- one to track when we went from non-zero to zero window
- one to track the reverse
- one counter incremented when we want to announce zero window,
  but can't because we would shrink current window.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index bbaba22..8d64a7e 100644 (file)
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -259,6 +259,9 @@ enum
        LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES, /* TCPSpuriousRtxHostQueues */
        LINUX_MIB_BUSYPOLLRXPACKETS,            /* BusyPollRxPackets */
        LINUX_MIB_TCPAUTOCORKING,               /* TCPAutoCorking */
+       LINUX_MIB_TCPFROMZEROWINDOWADV,         /* TCPFromZeroWindowAdv */
+       LINUX_MIB_TCPTOZEROWINDOWADV,           /* TCPToZeroWindowAdv */
+       LINUX_MIB_TCPWANTZEROWINDOWADV,         /* TCPWantZeroWindowAdv */
        __LINUX_MIB_MAX
 };
 

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index a6c8a80..99d2e9b 100644 (file)
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -280,6 +280,9 @@ static const struct snmp_mib snmp4_net_list[] = {
        SNMP_MIB_ITEM("TCPSpuriousRtxHostQueues", LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES),
        SNMP_MIB_ITEM("BusyPollRxPackets", LINUX_MIB_BUSYPOLLRXPACKETS),
        SNMP_MIB_ITEM("TCPAutoCorking", LINUX_MIB_TCPAUTOCORKING),
+       SNMP_MIB_ITEM("TCPFromZeroWindowAdv", LINUX_MIB_TCPFROMZEROWINDOWADV),
+       SNMP_MIB_ITEM("TCPToZeroWindowAdv", LINUX_MIB_TCPTOZEROWINDOWADV),
+       SNMP_MIB_ITEM("TCPWantZeroWindowAdv", LINUX_MIB_TCPWANTZEROWINDOWADV),
        SNMP_MIB_SENTINEL
 };
 

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 21e8a9f..c5eadec 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -269,6 +269,7 @@ EXPORT_SYMBOL(tcp_select_initial_window);
 static u16 tcp_select_window(struct sock *sk)
 {
        struct tcp_sock *tp = tcp_sk(sk);
+       u32 old_win = tp->rcv_wnd;
        u32 cur_win = tcp_receive_window(tp);
        u32 new_win = __tcp_select_window(sk);
 
@@ -281,6 +282,9 @@ static u16 tcp_select_window(struct sock *sk)
                 *
                 * Relax Will Robinson.
                 */
+               if (new_win == 0)
+                       NET_INC_STATS(sock_net(sk),
+                                     LINUX_MIB_TCPWANTZEROWINDOWADV);
                new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
        }
        tp->rcv_wnd = new_win;
@@ -298,8 +302,14 @@ static u16 tcp_select_window(struct sock *sk)
        new_win >>= tp->rx_opt.rcv_wscale;
 
        /* If we advertise zero window, disable fast path. */
-       if (new_win == 0)
+       if (new_win == 0) {
                tp->pred_flags = 0;
+               if (old_win)
+                       NET_INC_STATS(sock_net(sk),
+                                     LINUX_MIB_TCPTOZEROWINDOWADV);
+       } else if (old_win == 0) {
+               NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
+       }
 
        return new_win;
 }