slow_start_check.stp

# get the number of how much times was tcp_cwnd_restart called
# get real-time stats for cwnd
# use sysctl -w net.ipv4.tcp_slow_start_after_idle=0 (default 1)
# @ton31337

%{
#include <net/tcp.h>
%}

global count;
global etime;

function get_cwnd:long(sk:long)
%{
  struct tcp_sock *tp = tcp_sk((struct sock *)STAP_ARG_sk);
  u32 cwnd = tp->snd_cwnd;
  THIS->__retvalue = cwnd;
%}

probe begin
{
  etime = gettimeofday_s();
}

probe kernel.function("tcp_cwnd_restart")
{
  count++;
  printf("congestion window size: %d\n", get_cwnd($sk));
}

probe kernel.function("tcp_ack").return
{
  printf("Window size prior recovery: %d\n", $prior_cwnd);
}

probe timer.s(2)
{
  ansi_clear_screen();
}

probe end
{
  etime = gettimeofday_s() - etime;
  printf("\ntcp_cwnd_restart called %d times in %d seconds.\n", count, etime);
  delete count;
  delete etime;
}