[lttng-dev] [RFC PATCH lttng-ust] Introduce hash table for lttng_create_event_if_missing()

[Mathieu Desnoyers]

* Anik Mishra (anik.mishra at ericsson.com) wrote:
> -----Original Message-----
> From: Mathieu Desnoyers [mailto:mathieu.desnoyers at efficios.com] 
> Sent: January-16-13 10:15 AM
> To: lttng-dev at lists.lttng.org
> Subject: [lttng-dev] [RFC PATCH lttng-ust] Introduce hash table for lttng_create_event_if_missing()
> 
> [...]
> @@ -329,17 +331,19 @@ int lttng_event_create(const struct lttng_event_desc *desc,  {
> [...]
> -	/*
> -	 * 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) {
>  [...]
> 
> From other code:
> #define LTTNG_UST_EVENT_HT_BITS            6
> #define LTTNG_UST_EVENT_HT_SIZE            (1U << LTTNG_UST_EVENT_HT_BITS)
> 
> The way I read this,  if there's a substantial number of events,
> you're just dividing the time required by a constant 64. The
> complexity remains the same. Are you sure this is really a long term
> solution?

If we have much more than 10k _different_ TRACEPOINT_EVENT in the code,
we'll probably have other issues to fix.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com