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ctdb-io: Do not use sys_write to write to client sockets

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When sending messages to clients, ctdb checks for EAGAIN error code and
schedules next write in the subsequent event loop.  Using sys_write in
these places causes ctdb to loop hard till a client is able to read from
the socket.  With real time scheduling, ctdb daemon spins consuming 100%
of CPU trying to write to the client sockets.  This can be quite harmful
when running under VMs or machines with single CPU.

This regression was introduced when all read/write calls were replaced to
use sys_read/sys_write wrappers (c1558adeaa980fb4bd6177d36250ec8262e9b9fe).

The existing code backs off in case of EAGAIN failures and waits for an
event loop to process the write again.  This should give ctdb clients
a chance to get scheduled and to process the ctdb socket.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>

Autobuild-User(master): Martin Schwenke <martins@samba.org>
Autobuild-Date(master): Tue Feb 24 12:29:30 CET 2015 on sn-devel-104
This commit is contained in:
Amitay Isaacs 2015-02-23 12:38:11 +11:00 committed by Martin Schwenke
parent 84d4270c8e
commit 04a061e4d1
1 changed files with 3 additions and 3 deletions
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6
ctdb/common/ctdb_io.c
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@ -232,9 +232,9 @@ static void queue_io_write(struct ctdb_queue *queue)
struct ctdb_queue_pkt *pkt = queue->out_queue;
ssize_t n;
if (queue->ctdb->flags & CTDB_FLAG_TORTURE) {
n = sys_write(queue->fd, pkt->data, 1);
n = write(queue->fd, pkt->data, 1);
} else {
n = sys_write(queue->fd, pkt->data, pkt->length);
n = write(queue->fd, pkt->data, pkt->length);
}
if (n == -1 && errno != EAGAIN && errno != EWOULDBLOCK) {
@ -310,7 +310,7 @@ int ctdb_queue_send(struct ctdb_queue *queue, uint8_t *data, uint32_t length)
queue overhead. This relies on non-blocking sockets */
if (queue->out_queue == NULL && queue->fd != -1 &&
!(queue->ctdb->flags & CTDB_FLAG_TORTURE)) {
ssize_t n = sys_write(queue->fd, data, length2);
ssize_t n = write(queue->fd, data, length2);
if (n == -1 && errno != EAGAIN && errno != EWOULDBLOCK) {
talloc_free(queue->fde);
queue->fde = NULL;