[lttng-dev] [RFC PATCH lttng-ust] Introduce hash table for lttng_create_event_if_missing()
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Wed Jan 16 12:58:44 EST 2013
* Christian Babeux (christian.babeux at efficios.com) wrote:
> I was able to reproduce this overhead issue on my machine.
> This patch fixed it.
OK! Patch pushed into lttng-ust master and stable-2.1 branches.
Thanks,
Mathieu
>
> Acked-by: Christian Babeux <christian.babeux at efficios.com>
>
> On Wed, Jan 16, 2013 at 10:14 AM, Mathieu Desnoyers
> <mathieu.desnoyers at efficios.com> wrote:
> > 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
> >
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > ---
> > diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
> > index 095fb1e..1db8e58 100644
> > --- 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 5e6c90c..f70c65f 100644
> > --- 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;
> > }
> >
> > --
> > Mathieu Desnoyers
> > EfficiOS Inc.
> > http://www.efficios.com
> >
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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