Introduce hash table for lttng_create_event_if_missing()

lttng_create_event_if_missing() takes a lot of CPU time with stress-test
applications containing 1000 different TRACEPOINT_EVENT() and 1000
individual tracepoint() call-site.

With tracing disabled:

time ./AppWith1000_lines_TP 0

real    0m2.487s
user    0m2.424s
sys     0m0.000s

Introducing this hash table cuts the overhead very significantly when
tracing is enabled:

Before patch:

 72.16%  AppWith1000_lin  liblttng-ust.so.0.0.0             [.] lttng_create_event_if_missing
 25.64%  AppWith1000_lin  AppWith1000_lines_TP              [.] a(int)

time ./AppWith1000_lines_TP 0

real    0m7.946s
user    0m7.864s
sys     0m0.000s

After patch:

 89.13%  AppWith1000_lin  AppWith1000_lines_TP              [.] a(int)
  3.30%  AppWith1000_lin  liblttng-ust.so.0.0.0             [.] lttng_create_event_if_missing

time ./AppWith1000_lines_TP 0

real    0m2.762s
user    0m2.692s
sys     0m0.004s

Acked-by: David Goulet <dgoulet@efficios.com>
Acked-by: Christian Babeux <christian.babeux@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
index 095fb1ef1482ac954be5aa88ed06b55ede45a571..1db8e585f1f5d86dac05f7f75b17ba8c723e1ec5 100644 (file)
--- a/include/lttng/ust-events.h
+++ b/include/lttng/ust-events.h
@@ -362,6 +362,7 @@ struct lttng_event {
        int has_enablers_without_bytecode;
        /* Backward references: list of lttng_enabler_ref (ref to enablers) */
        struct cds_list_head enablers_ref_head;
+       struct cds_hlist_node hlist;    /* session ht of events */
 };
 
 struct channel;
@@ -467,6 +468,7 @@ struct lttng_session {
        /* New UST 2.1 */
        /* List of enablers */
        struct cds_list_head enablers_head;
+       struct lttng_ust_event_ht events_ht;    /* ht of events */
 };
 
 struct lttng_transport {

diff --git a/liblttng-ust/lttng-events.c b/liblttng-ust/lttng-events.c
index 5e6c90cbd8383b2324e5cb73ed9db74395f993f9..f70c65f5405c83106d4527c366431698f2fc7841 100644 (file)
--- a/liblttng-ust/lttng-events.c
+++ b/liblttng-ust/lttng-events.c
@@ -127,7 +127,7 @@ void synchronize_trace(void)
 struct lttng_session *lttng_session_create(void)
 {
        struct lttng_session *session;
-       int ret;
+       int ret, i;
 
        session = zmalloc(sizeof(struct lttng_session));
        if (!session)
@@ -135,6 +135,8 @@ struct lttng_session *lttng_session_create(void)
        CDS_INIT_LIST_HEAD(&session->chan_head);
        CDS_INIT_LIST_HEAD(&session->events_head);
        CDS_INIT_LIST_HEAD(&session->enablers_head);
+       for (i = 0; i < LTTNG_UST_EVENT_HT_SIZE; i++)
+               CDS_INIT_HLIST_HEAD(&session->events_ht.table[i]);
        ret = lttng_ust_uuid_generate(session->uuid);
        if (ret != 0) {
                session->uuid[0] = '\0';
@@ -329,17 +331,19 @@ int lttng_event_create(const struct lttng_event_desc *desc,
 {
        const char *event_name = desc->name;
        struct lttng_event *event;
+       struct cds_hlist_head *head;
+       struct cds_hlist_node *node;
        int ret = 0;
+       size_t name_len = strlen(event_name);
+       uint32_t hash;
 
        if (chan->used_event_id == -1U) {
                ret = -ENOMEM;
                goto full;
        }
-       /*
-        * This is O(n^2) (for each event, the loop is called at event
-        * creation). Might require a hash if we have lots of events.
-        */
-       cds_list_for_each_entry(event, &chan->session->events_head, node) {
+       hash = jhash(event_name, name_len, 0);
+       head = &chan->session->events_ht.table[hash & (LTTNG_UST_EVENT_HT_SIZE - 1)];
+       cds_hlist_for_each_entry(event, node, head, hlist) {
                assert(event->desc);
                if (!strncmp(event->desc->name,
                                desc->name,
@@ -380,6 +384,7 @@ int lttng_event_create(const struct lttng_event_desc *desc,
        if (ret)
                goto statedump_error;
        cds_list_add(&event->node, &chan->session->events_head);
+       cds_hlist_add_head(&event->hlist, head);
        return 0;
 
 statedump_error:
@@ -499,17 +504,24 @@ void lttng_create_event_if_missing(struct lttng_enabler *enabler)
        cds_list_for_each_entry(probe_desc, probe_list, head) {
                for (i = 0; i < probe_desc->nr_events; i++) {
                        int found = 0, ret;
+                       struct cds_hlist_head *head;
+                       struct cds_hlist_node *node;
+                       const char *event_name;
+                       size_t name_len;
+                       uint32_t hash;
 
                        desc = probe_desc->event_desc[i];
                        if (!lttng_desc_match_enabler(desc, enabler))
                                continue;
+                       event_name = desc->name;
+                       name_len = strlen(event_name);
 
                        /*
-                        * For each event in session event list,
-                        * check if already created.
+                        * Check if already created.
                         */
-                       cds_list_for_each_entry(event,
-                                       &session->events_head, node) {
+                       hash = jhash(event_name, name_len, 0);
+                       head = &session->events_ht.table[hash & (LTTNG_UST_EVENT_HT_SIZE - 1)];
+                       cds_hlist_for_each_entry(event, node, head, hlist) {
                                if (event->desc == desc)
                                        found = 1;
                        }