unix_dgram_recvmsg wakeups [test results & programs]

Rainer Weikusat
2015-11-26T19:19:20Z

[to be followed by a patch]

Currently, unix_dgram_recvmsg does a wake up on the peer_wait queue of a
socket after every received datagram. This seems excessive, especially
considering that only SOCK_DGRAM client sockets in an n:1 asssociation
with a server socket ever wait for the associated condition.

Values are based on 500 runs of either test program.

SOCK_SEQPACKET throughput (B/s)

stock patched
---------------------------------------------------------------
avg 14714579.91 17898665.25 +26.64%
median 14409539.95 16429584.38 +14.02%
dev 1582631.52 3475160.01

min 13588814.36 14864694.12
max 25960203 27264811.18

SOCK_DGRAM 100 clients/ 1 server (B/s)

stock patched
---------------------------------------------------------------
avg 57394.06 58222.93 +1.44%
median 55878.12 56993.55 +2%
dev 3540.02 3488.49

min 54167.33 53165.51
max 67971.15 66466.99

SOCK_SEQPACKET test program
---------------------------
#include <inttypes.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <unistd.h>

enum {
MSG_SZ = 16,
MSGS = 1000000
};

static char msg[MSG_SZ];

static uint64_t tv2u(struct timeval *tv)
{
uint64_t u;

u = tv->tv_sec;
u *= 1000000;
return u + tv->tv_usec;
}

int main(void)
{
struct timeval start, stop;
uint64_t t_diff;
double rate;
int sks[2];
unsigned remain;
char buf[MSG_SZ];

socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sks);

if (fork() == 0) {
close(*sks);

gettimeofday(&start, 0);
while (read(sks[1], buf, sizeof(buf)) > 0);
gettimeofday(&stop, 0);

t_diff = tv2u(&stop);
t_diff -= tv2u(&start);
rate = MSG_SZ * MSGS;
rate /= t_diff;
rate *= 1000000;
printf("%f\n", rate);

fflush(stdout);
_exit(0);
}

close(sks[1]);

remain = MSGS;
do write(*sks, msg, sizeof(msg)); while (--remain);
close(*sks);

wait(NULL);
return 0;
}
--------------------------

SOCK_DGRAM test program
-----------------------
#include <inttypes.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/poll.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <unistd.h>

#define SERVER_ADDR "\0dgt-2"

enum {
MSG_SZ = 16,
MSGS = 1000
};

static char msg[MSG_SZ];
static struct sockaddr_un server_sun;

static uint64_t tv2u(struct timeval *tv)
{
uint64_t u;

u = tv->tv_sec;
u *= 1000000;
return u + tv->tv_usec;
}

static void server(int sk, unsigned want)
{
struct timeval start, stop;
char buf[MSG_SZ];
uint64_t t_diff;
double rate;

gettimeofday(&start, 0);
do read(sk, buf, sizeof(buf)); while (--want);
gettimeofday(&stop, 0);

t_diff = tv2u(&stop);
t_diff -= tv2u(&start);
rate = MSG_SZ * MSGS;
rate /= t_diff;
rate *= 1000000;
printf("%f\n", rate);
}

static void client(void)
{
unsigned remain;
int sk;

sk = socket(AF_UNIX, SOCK_DGRAM, 0);
connect(sk, (struct sockaddr *)&server_sun, sizeof(server_sun));

remain = MSGS;
do write(sk, msg, sizeof(msg)); while (--remain);

_exit(0);
}

int main(int argc, char **argv)
{
unsigned n_clients, want;
int sk;

n_clients = atoi(argv[1]);

server_sun.sun_family = AF_UNIX;
memcpy(server_sun.sun_path, SERVER_ADDR, sizeof(SERVER_ADDR));
sk = socket(AF_UNIX, SOCK_DGRAM, 0);
bind(sk, (struct sockaddr *)&server_sun, sizeof(server_sun));

want = n_clients * MSGS;
do if (fork() == 0) client(); while (--n_clients);

server(sk, want);
return 0;
}