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socket: break receive loop if there are no more outstanding PDUs

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If the length of iscsi->waitpdu and iscsi->inqueue are the same
then except for any target initiated NOPs or async messages
we should have received any and all possible pdus from this
socket and can abort early.

This avoids running the loop one more time just to fail with EAGAIN
at the recs/readv. Just avoiding that recv/readv syscall will shave
at least 10us off this function and thus the latency.

Suggested-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
This commit is contained in:
Peter Lieven
2017-01-03 11:13:06 +01:00
parent b81e9a28a6
commit e058e825bf
1 changed files with 5 additions and 3 deletions
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8
lib/socket.c
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@@ -567,6 +567,9 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
{
struct iscsi_in_pdu *in;
ssize_t data_size, count, padding_size;
int waitpdu_len, inqueue_len = 0;
ISCSI_LIST_LENGTH(&iscsi->waitpdu, waitpdu_len);
do {
if (iscsi->incoming == NULL) {
@@ -638,7 +641,6 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
}
count = recv(iscsi->fd, buf, count, 0);
}
if (count == 0) {
/* remote side has closed the socket. */
return -1;
@@ -652,7 +654,6 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
iscsi_get_error(iscsi));
return -1;
}
in->data_pos += count;
}
@@ -661,8 +662,9 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
}
ISCSI_LIST_ADD_END(&iscsi->inqueue, in);
inqueue_len++;
iscsi->incoming = NULL;
} while (iscsi->is_loggedin && iscsi->tcp_nonblocking);
} while (iscsi->tcp_nonblocking && inqueue_len < waitpdu_len && iscsi->is_loggedin);
while (iscsi->inqueue != NULL) {
struct iscsi_in_pdu *current = iscsi->inqueue;