Re: [PATCH 1/3] jump label: add enabled/disabled state to jumplabel key entries

[Steven Rostedt]

On Tue, 2010-11-23 at 18:43 -0500, Mathieu Desnoyers wrote:
> * Jason Baron (jbaron@xxxxxxxxxx) wrote:
> [...]
> > +static void update_jump_label_module(struct module *mod)
> > +{
> > +	struct hlist_head *head;
> > +	struct hlist_node *node, *node_next, *module_node, *module_node_next;
> > +	struct jump_label_entry *e;
> > +	struct jump_label_module_entry *e_module;
> > +	struct jump_entry *iter;
> > +	int i, count;
> > +
> > +	/* if the module doesn't have jump label entries, just return */
> > +	if (!mod->num_jump_entries)
> > +		return;
> > +
> > +	for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
> > +		head = &jump_label_table[i];
> > +		hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
> > +			if (!e->enabled)
> > +				continue;
> > +			hlist_for_each_entry_safe(e_module, module_node,
> > +						  module_node_next,
> > +						  &(e->modules), hlist) {
> > +				if (e_module->mod != mod)
> > +					continue;
> 
> Ouch.
> 
> Could you iterate on the loaded/unloaded module jump labels and do hash
> table lookups rather than doing this O(n^3) iteration ?

This does not look O(n^3) to me.

It's a hash table, thus the first two loops is just iterating O(n) items
in the hash.

And the third loop is all the modules that use a particular event.

So it is O(n*m)  where n is the number of events, and m is the number of
modules attached to the events. And that's only if all events are used
by those modules. The actual case is much smaller.

-- Steve


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