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Optimize lwip_selscan()

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This makes a couple of simple re-arrangements in lwip_selscan() that
should improve performance in the following ways:

  1) The old code linearly walked all sockets to maxfd regardless of
     whether they were set in the fd set. The process involved
     acquiring sys arch protect, looking up the socket, and then
     checking if the socket was present in any of the fd sets. On
     systems with lots of sockets and a heavy SYS_ARCH_PROTECT
     infrastructure (a mutex) this can result in a lot of extra work.
     Now we skip this process for any fd that is not in the input sets
  2) If the socket from tryget_socket() is NULL we no longer continue
     and compare the input fd sets with a zeroed out set of events
  3) We no longer need to zero out our event sets because they are
     only accessed when tryget_socket() is successful

lwip_selscan() is called at most once per select call and sometimes up to three times
This commit is contained in:
Joel Cunningham 2016-02-17 16:33:35 -06:00
parent 9a97a80efc
commit ea94549cb2
1 changed files with 34 additions and 28 deletions
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62
src/api/sockets.c
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@ -1315,38 +1315,44 @@ lwip_selscan(int maxfdp1, fd_set *readset_in, fd_set *writeset_in, fd_set *excep
/* Go through each socket in each list to count number of sockets which
currently match */
for (i = LWIP_SOCKET_OFFSET; i < maxfdp1; i++) {
void* lastdata = NULL;
s16_t rcvevent = 0;
u16_t sendevent = 0;
u16_t errevent = 0;
/* if this FD is not in the set, continue */
if (!(readset_in && FD_ISSET(i, readset_in)) &&
!(writeset_in && FD_ISSET(i, writeset_in)) &&
!(exceptset_in && FD_ISSET(i, exceptset_in))) {
continue;
}
/* First get the socket's status (protected)... */
SYS_ARCH_PROTECT(lev);
sock = tryget_socket(i);
if (sock != NULL) {
lastdata = sock->lastdata;
rcvevent = sock->rcvevent;
sendevent = sock->sendevent;
errevent = sock->errevent;
}
SYS_ARCH_UNPROTECT(lev);
/* ... then examine it: */
/* See if netconn of this socket is ready for read */
if (readset_in && FD_ISSET(i, readset_in) && ((lastdata != NULL) || (rcvevent > 0))) {
FD_SET(i, &lreadset);
LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_selscan: fd=%d ready for reading\n", i));
nready++;
}
/* See if netconn of this socket is ready for write */
if (writeset_in && FD_ISSET(i, writeset_in) && (sendevent != 0)) {
FD_SET(i, &lwriteset);
LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_selscan: fd=%d ready for writing\n", i));
nready++;
}
/* See if netconn of this socket had an error */
if (exceptset_in && FD_ISSET(i, exceptset_in) && (errevent != 0)) {
FD_SET(i, &lexceptset);
LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_selscan: fd=%d ready for exception\n", i));
nready++;
void* lastdata = sock->lastdata;
s16_t rcvevent = sock->rcvevent;
u16_t sendevent = sock->sendevent;
u16_t errevent = sock->errevent;
SYS_ARCH_UNPROTECT(lev);
/* ... then examine it: */
/* See if netconn of this socket is ready for read */
if (readset_in && FD_ISSET(i, readset_in) && ((lastdata != NULL) || (rcvevent > 0))) {
FD_SET(i, &lreadset);
LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_selscan: fd=%d ready for reading\n", i));
nready++;
}
/* See if netconn of this socket is ready for write */
if (writeset_in && FD_ISSET(i, writeset_in) && (sendevent != 0)) {
FD_SET(i, &lwriteset);
LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_selscan: fd=%d ready for writing\n", i));
nready++;
}
/* See if netconn of this socket had an error */
if (exceptset_in && FD_ISSET(i, exceptset_in) && (errevent != 0)) {
FD_SET(i, &lexceptset);
LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_selscan: fd=%d ready for exception\n", i));
nready++;
}
} else {
SYS_ARCH_UNPROTECT(lev);
/* continue on to next FD in list */
}
}
/* copy local sets to the ones provided as arguments */