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Speed up DNS by avoiding a system call if possible

This commit is contained in:
Ulrich Drepper 2012-03-30 07:42:29 -04:00
parent 1d39e35923
commit c030f70c87
2 changed files with 86 additions and 17 deletions
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3
ChangeLog
View File

@ -1,5 +1,8 @@
2012-03-30 Ulrich Drepper <drepper@gmail.com>
* resolv/res_send.c (send_dg): Use sendmmsg if we have to write two
requests to save a system call.
* sysdeps/unix/sysv/linux/bits/socket.h (struct mmsghdr): Fix up
comments for sendmmsg.

100
resolv/res_send.c
View File

@ -1013,8 +1013,9 @@ send_dg(res_state statp,
seconds /= statp->nscount;
if (seconds <= 0)
seconds = 1;
bool single_request = (statp->options & RES_SNGLKUP) != 0;
bool single_request_reopen = (statp->options & RES_SNGLKUPREOP) != 0;
bool single_request = (((statp->options & RES_SNGLKUP) != 0)
| single_request_reopen);
int save_gotsomewhere = *gotsomewhere;
int retval;
@ -1100,24 +1101,89 @@ send_dg(res_state statp,
}
__set_errno (0);
if (pfd[0].revents & POLLOUT) {
ssize_t sr;
if (nwritten != 0)
sr = send (pfd[0].fd, buf2, buflen2, MSG_NOSIGNAL);
else
sr = send (pfd[0].fd, buf, buflen, MSG_NOSIGNAL);
#ifndef __ASSUME_SENDMMSG
static int have_sendmmsg;
#else
# define have_sendmmsg 1
#endif
if (have_sendmmsg >= 0 && nwritten == 0 && buf2 != NULL
&& !single_request)
{
struct iovec iov[2];
struct mmsghdr reqs[2];
reqs[0].msg_hdr.msg_name = NULL;
reqs[0].msg_hdr.msg_namelen = 0;
reqs[0].msg_hdr.msg_iov = &iov[0];
reqs[0].msg_hdr.msg_iovlen = 1;
iov[0].iov_base = (void *) buf;
iov[0].iov_len = buflen;
reqs[0].msg_hdr.msg_control = NULL;
reqs[0].msg_hdr.msg_controllen = 0;
if (sr != buflen) {
if (errno == EINTR || errno == EAGAIN)
goto recompute_resend;
Perror(statp, stderr, "send", errno);
reqs[1].msg_hdr.msg_name = NULL;
reqs[1].msg_hdr.msg_namelen = 0;
reqs[1].msg_hdr.msg_iov = &iov[1];
reqs[1].msg_hdr.msg_iovlen = 1;
iov[1].iov_base = (void *) buf2;
iov[1].iov_len = buflen2;
reqs[1].msg_hdr.msg_control = NULL;
reqs[1].msg_hdr.msg_controllen = 0;
int ndg = sendmmsg (pfd[0].fd, reqs, 2, MSG_NOSIGNAL);
if (__builtin_expect (ndg == 2, 1))
{
assert (reqs[0].msg_len == buflen);
assert (reqs[1].msg_len == buflen2);
pfd[0].events = POLLIN;
nwritten += 2;
}
else if (ndg == 1 && reqs[0].msg_len == buflen)
goto just_one;
else if (errno == EINTR || errno == EAGAIN)
goto recompute_resend;
else
{
#ifndef __ASSUME_SENDMMSG
if (have_sendmmsg == 0)
{
if (errno == ENOSYS)
{
have_sendmmsg = -1;
goto try_send;
}
have_sendmmsg = 1;
}
#endif
Perror(statp, stderr, "sendmmsg", errno);
goto err_out;
}
if (nwritten != 0 || buf2 == NULL
|| single_request || single_request_reopen)
pfd[0].events = POLLIN;
}
}
else
pfd[0].events = POLLIN | POLLOUT;
++nwritten;
{
ssize_t sr;
#ifndef __ASSUME_SENDMMSG
try_send:
#endif
if (nwritten != 0)
sr = send (pfd[0].fd, buf2, buflen2, MSG_NOSIGNAL);
else
sr = send (pfd[0].fd, buf, buflen, MSG_NOSIGNAL);
if (sr != buflen) {
if (errno == EINTR || errno == EAGAIN)
goto recompute_resend;
Perror(statp, stderr, "send", errno);
goto err_out;
}
just_one:
if (nwritten != 0 || buf2 == NULL || single_request)
pfd[0].events = POLLIN;
else
pfd[0].events = POLLIN | POLLOUT;
++nwritten;
}
goto wait;
} else if (pfd[0].revents & POLLIN) {
int *thisanssizp;
@ -1327,7 +1393,7 @@ send_dg(res_state statp,
recvresp2 = 1;
/* Repeat waiting if we have a second answer to arrive. */
if ((recvresp1 & recvresp2) == 0) {
if (single_request || single_request_reopen) {
if (single_request) {
pfd[0].events = POLLOUT;
if (single_request_reopen) {
__res_iclose (statp, false);