Chris Wedgwood wrote:
>
> You can measure this latency; and it's indeed very low (lmbench gives
> 28 usecs on one of my machines).
>
> If you don't see this I would suspect an application bug -- can you
> use strace or some such and confirm this is not the case?
OK, two new data points (thanks for staying with me here):
1. The problem only occurs when traffic is travelling over DIFFERENT
sockets (i.e. A->B->C->D... or A->B->A but using a separate socket for
traffic in each direction).
2. I wrote a very ugly program (attached) to reproduce the problem. Lest
you think ill of me, most of this isn't actual code I wrote (the actual
program that first reproduced the problem was in C++). Just run
sockperf localhost 54321 54322
sockperf localhost 54322 54321 1
to see it in action.
-- Mike Lindner --------------EF2174A08E061DBE445265D0 Content-Type: text/plain; charset=us-ascii; name="sockperf.c" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="sockperf.c"#include <fcntl.h> #include <memory.h> #include <netdb.h> #include <netinet/in.h> #include <signal.h> #include <stdio.h> #include <sys/select.h> #include <sys/types.h> #include <sys/socket.h> #include <varargs.h> #include <netinet/in.h> #include <netdb.h> #include <errno.h> #include <arpa/inet.h> #include <sys/time.h> #include <unistd.h>
#ifndef INADDR_NONE #define INADDR_NONE ~0 #endif
void errexit(format, va_alist) char *format; va_dcl { va_list args; va_start(args); vfprintf(stderr, format, args); va_end(args); exit(1); }
/* * passivesock - allocate & bind a server socket using TCP or UDP */
int passivesock( service, protocol, qlen ) char *service; /* service associeted with the desired port */ char *protocol; /* name of protocol to use ("tcp" or "udp") */ int qlen; /* maximum length of the server request queue */ { struct servent *pse; struct protoent *ppe; struct sockaddr_in sin; int s, type; int one = 1;
bzero((char *) & sin, sizeof(sin)); sin.sin_family = AF_INET; sin.sin_addr.s_addr = INADDR_ANY;
/* Map service name to port number */ if ( pse = getservbyname(service, protocol) ) sin.sin_port = htons(ntohs((u_short)pse->s_port)); else if ( (sin.sin_port = htons((u_short)atoi(service))) == 0 ) errexit("can't get \"%s\" service entry\n", service);
/* Map protocol name to protocol number */ if ( (ppe = getprotobyname(protocol)) == 0) errexit("can't get \"%s\" protocol entry\n", protocol);
/* Use protocol to chose a socket type */ if (strcmp(protocol, "udp") == 0) type = SOCK_DGRAM; else type = SOCK_STREAM;
/* Allocate a socket */ s = socket(PF_INET, type, ppe->p_proto); if (s < 0 ) errexit("can't create socket: %s\n", strerror(errno));
setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)); /* Bind the socket */ if (bind(s, (struct sockaddr *) & sin, sizeof(sin)) < 0) errexit("can't bind to %s port: %s\n", service, strerror(errno)); if (type == SOCK_STREAM && listen(s, qlen) < 0) errexit("can't listen on %s port: %s\n", service, strerror(errno)); return s; }
int connectsock(host, service, protocol) char *host; char *service; char *protocol; { struct hostent *phe; struct servent *pse; struct protoent *ppe; struct sockaddr_in sin; int s, type;
memset(&sin, 0, sizeof(sin)); if (pse = getservbyname(service, protocol)) sin.sin_port = pse->s_port; else if ((sin.sin_port = htons((u_short) atoi(service))) == 0) { fprintf(stderr, "can't get '%s' service entry\n", service); exit(1); } if (phe = gethostbyname(host)) memcpy((char *) &sin.sin_addr, phe->h_addr, phe->h_length); else if ((sin.sin_addr.s_addr = inet_addr(host)) == INADDR_NONE) { fprintf(stderr, "can't get '%s' host entry\n", host); exit(1); } /* if (ppe = getprotobyname(protocol)) { fprintf(stderr, "can't get '%s' protocol entry\n", protocol); exit(1); } if (strcmp(protocol, "udp") == 0) type = SOCK_DGRAM; else type = SOCK_STREAM; */ sin.sin_family = AF_INET; s = socket(AF_INET, SOCK_STREAM, 6); if (s < 0) { perror("can't create socket\n"); exit(1); } if (connect(s, (struct sockaddr *) &sin, sizeof(sin)) < 0) { perror("can't connect to socket"); exit(1); } return s; }
void pingpong(int r, int s, int ping) { struct timeval then; struct timeval now; fd_set fds; fd_set readfds; int pings = 0; FD_ZERO(&fds); FD_SET(r, &fds); gettimeofday(&then, 0); if (ping) { send(s, ".", 1, 0); pings++; } readfds = fds; while (select(r+1, &readfds, 0, 0, 0) > 0) { if (FD_ISSET(r, &readfds)) { char buf[1]; int n = read(r, buf, sizeof(buf)); if (n <= 0) { break; } else { if (pings++ < 1000) { send(s, ".", 1, 0); } else { break; } } } else { fprintf(stderr, "fd not set!\n"); } readfds = fds; } gettimeofday(&now, 0); fprintf(stderr, "elapsed time for 1000 pingpongs is %g\n", now.tv_sec - then.tv_sec + (now.tv_usec - then.tv_usec) / 1000000.0); fprintf(stderr, "closing %d\n", r); close(r); fprintf(stderr, "closing %d\n", s); close(s); }
main(argc, argv) int argc; char **argv; { char buf[1024]; int n; int s; int f; if (argc < 3) { errexit("usage: %s host port1 port2 [initiate]\n", argv[0]); } signal(SIGPIPE, SIG_IGN); f = passivesock(argv[2], "tcp", 2); if (f < 0) { errexit("listen failed: %s\n", strerror(errno)); } for ( ; ; ) { struct sockaddr_in fsin; int alen = sizeof(fsin); if (argc < 5) { int r = accept(f, (struct sockaddr *) &fsin, &alen); int s = connectsock(argv[1], argv[3], "tcp"); if (r < 0) errexit("accept failed: %s\n", strerror(errno)); if (s < 0) errexit("connect failed: %s\n", strerror(errno)); pingpong(r, s, 0); } else { int s = connectsock(argv[1], argv[3], "tcp"); int r = accept(f, (struct sockaddr *) &fsin, &alen); if (r < 0) errexit("accept failed: %s\n", strerror(errno)); if (s < 0) errexit("connect failed: %s\n", strerror(errno)); pingpong(r, s, 1); break; } } return 0; }
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