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use reference counter for pipeline groups (v3)

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Track pipeline groups using a shared reference counter
instead of a linked list.

(cherry picked from commit 31f392db20207a1b05d6286c3c56f76c8d69e574)
(cherry picked from commit 2211120222)
This commit is contained in:
Michał Kępień
2019-01-17 15:53:38 +01:00
committed by Ondřej Surý
parent d989a8b38e
commit 3c0f8d9146
2 changed files with 110 additions and 63 deletions
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171
lib/ns/client.c
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@@ -316,6 +316,75 @@ read_settimeout(ns_client_t *client, bool newconn) {
}
}
/*%
* Allocate a reference counter that will track the number of client structures
* using the TCP connection that 'client' called accept() for. This counter
* will be shared between all client structures associated with this TCP
* connection.
*/
static void
pipeline_init(ns_client_t *client) {
isc_refcount_t *refs;
REQUIRE(client->pipeline_refs == NULL);
/*
* A global memory context is used for the allocation as different
* client structures may have different memory contexts assigned and a
* reference counter allocated here might need to be freed by a
* different client. The performance impact caused by memory context
* contention here is expected to be negligible, given that this code
* is only executed for TCP connections.
*/
refs = isc_mem_allocate(client->sctx->mctx, sizeof(*refs));
isc_refcount_init(refs, 1);
client->pipeline_refs = refs;
}
/*%
* Increase the count of client structures using the TCP connection that
* 'source' is associated with and put a pointer to that count in 'target',
* thus associating it with the same TCP connection.
*/
static void
pipeline_attach(ns_client_t *source, ns_client_t *target) {
int old_refs;
REQUIRE(source->pipeline_refs != NULL);
REQUIRE(target->pipeline_refs == NULL);
old_refs = isc_refcount_increment(source->pipeline_refs);
INSIST(old_refs > 0);
target->pipeline_refs = source->pipeline_refs;
}
/*%
* Decrease the count of client structures using the TCP connection that
* 'client' is associated with. If this is the last client using this TCP
* connection, free the reference counter and return true; otherwise, return
* false.
*/
static bool
pipeline_detach(ns_client_t *client) {
isc_refcount_t *refs;
int old_refs;
REQUIRE(client->pipeline_refs != NULL);
refs = client->pipeline_refs;
client->pipeline_refs = NULL;
old_refs = isc_refcount_decrement(refs);
INSIST(old_refs > 0);
if (old_refs == 1) {
isc_mem_free(client->sctx->mctx, refs);
return (true);
}
return (false);
}
/*%
* Check for a deactivation or shutdown request and take appropriate
* action. Returns true if either is in progress; in this case
@@ -438,6 +507,40 @@ exit_check(ns_client_t *client) {
client->tcpmsg_valid = false;
}
if (client->tcpquota != NULL) {
if (client->pipeline_refs == NULL ||
pipeline_detach(client))
{
/*
* Only detach from the TCP client quota if
* there are no more client structures using
* this TCP connection.
*
* Note that we check 'pipeline_refs' and not
* 'pipelined' because in some cases (e.g.
* after receiving a request with an opcode
* different than QUERY) 'pipelined' is set to
* false after the reference counter gets
* allocated in pipeline_init() and we must
* still drop our reference as failing to do so
* would prevent the reference counter itself
* from being freed.
*/
isc_quota_detach(&client->tcpquota);
} else {
/*
* There are other client structures using this
* TCP connection, so we cannot detach from the
* TCP client quota to prevent excess TCP
* connections from being accepted. However,
* this client structure might later be reused
* for accepting new connections and thus must
* have its 'tcpquota' field set to NULL.
*/
client->tcpquota = NULL;
}
}
if (client->tcpsocket != NULL) {
CTRACE("closetcp");
isc_socket_detach(&client->tcpsocket);
@@ -451,44 +554,6 @@ exit_check(ns_client_t *client) {
}
}
if (client->tcpquota != NULL) {
/*
* If we are not in a pipeline group, or
* we are the last client in the group, detach from
* tcpquota; otherwise, transfer the quota to
* another client in the same group.
*/
if (!ISC_LINK_LINKED(client, glink) ||
(client->glink.next == NULL &&
client->glink.prev == NULL))
{
isc_quota_detach(&client->tcpquota);
} else if (client->glink.next != NULL) {
INSIST(client->glink.next->tcpquota == NULL);
client->glink.next->tcpquota = client->tcpquota;
client->tcpquota = NULL;
} else {
INSIST(client->glink.prev->tcpquota == NULL);
client->glink.prev->tcpquota = client->tcpquota;
client->tcpquota = NULL;
}
}
/*
* Unlink from pipeline group.
*/
if (ISC_LINK_LINKED(client, glink)) {
if (client->glink.next != NULL) {
client->glink.next->glink.prev =
client->glink.prev;
}
if (client->glink.prev != NULL) {
client->glink.prev->glink.next =
client->glink.next;
}
ISC_LINK_INIT(client, glink);
}
if (client->timerset) {
(void)isc_timer_reset(client->timer,
isc_timertype_inactive,
@@ -3106,6 +3171,7 @@ client_create(ns_clientmgr_t *manager, ns_client_t **clientp) {
client->mortal = false;
client->sendcb = NULL;
client->pipelined = false;
client->pipeline_refs = NULL;
client->tcpquota = NULL;
client->recursionquota = NULL;
client->interface = NULL;
@@ -3127,7 +3193,6 @@ client_create(ns_clientmgr_t *manager, ns_client_t **clientp) {
client->formerrcache.id = 0;
ISC_LINK_INIT(client, link);
ISC_LINK_INIT(client, rlink);
ISC_LINK_INIT(client, glink);
ISC_QLINK_INIT(client, ilink);
client->keytag = NULL;
client->keytag_len = 0;
@@ -3316,6 +3381,7 @@ client_newconn(isc_task_t *task, isc_event_t *event) {
!dns_acl_allowed(&netaddr, NULL,
client->sctx->keepresporder, env)))
{
pipeline_init(client);
client->pipelined = true;
}
@@ -3786,37 +3852,18 @@ get_worker(ns_clientmgr_t *manager, ns_interface_t *ifp, isc_socket_t *sock,
client->newstate = client->state = NS_CLIENTSTATE_WORKING;
INSIST(client->recursionquota == NULL);
client->sctx = manager->sctx;
/*
* Transfer TCP quota to the new client.
*/
INSIST(client->tcpquota == NULL);
INSIST(oldclient->tcpquota != NULL);
client->tcpquota = oldclient->tcpquota;
oldclient->tcpquota = NULL;
/*
* Link to a pipeline group, creating it if needed.
*/
if (!ISC_LINK_LINKED(oldclient, glink)) {
oldclient->glink.next = NULL;
oldclient->glink.prev = NULL;
}
client->glink.next = oldclient->glink.next;
client->glink.prev = oldclient;
if (oldclient->glink.next != NULL) {
oldclient->glink.next->glink.prev = client;
}
oldclient->glink.next = client;
client->tcpquota = &client->sctx->tcpquota;
client->dscp = ifp->dscp;
client->attributes |= NS_CLIENTATTR_TCP;
client->pipelined = true;
client->mortal = true;
client->sendcb = NULL;
client->rcode_override = -1; /* not set */
pipeline_attach(oldclient, client);
client->pipelined = true;
isc_socket_attach(ifp->tcpsocket, &client->tcplistener);
isc_socket_attach(sock, &client->tcpsocket);
isc_socket_setname(client->tcpsocket, "worker-tcp", NULL);