> Jan Hubicka <hubi...@ucw.cz> writes:
>
> > Hi,
> > this patch started as experiment moving hash_table_mod1 inline because it
> > shows
> > high in streaming profiles and it represents a branch-less code that is good
> > to schedule to surrounding instructions.
>
> FWIW with a good modern hash function it shouldn't be needed to have
> prime hash table sizes anymore. Without that just a power of two size
> can be used, so it would be just a mask.
>
> I considered this last time I messed with hashes, but I didn't actually
> see this function as beening hot.
If I measure the wpa-stream thread only, I get about 18% in the hashtable
lookup:
18.33% lto1-wpa-stream lto1 [.]
hash_table<hash_map<tree_node*, unsigned int,
default_hashmap_traits>::hash_entry, xcallocator,
true>::find_with_hash(tree_node* const&, uďż˝
9.53% lto1-wpa-stream lto1 [.]
DFS::DFS_write_tree(output_block*, DFS::sccs*, tree_node*, bool, bool, bool)
ďż˝
8.43% lto1-wpa-stream lto1 [.] linemap_lookup(line_maps*,
unsigned int)
ďż˝
5.81% lto1-wpa-stream lto1 [.]
streamer_write_uhwi_stream(lto_output_stream*, unsigned long)
ďż˝
4.47% lto1-wpa-stream lto1 [.] lto_output_tree(output_block*,
tree_node*, bool, bool)
ďż˝
3.11% lto1-wpa-stream libc-2.13.so [.] _int_malloc
ďż˝
2.85% lto1-wpa-stream lto1 [.]
DFS::DFS_write_tree_body(output_block*, tree_node*, DFS::sccs*, bool, bool)
ďż˝
I am not quite sure hash function is the bottleneck though - I would more
expect it to be cache miss sink. It may be interesting though to replace it by
something more resonable than this pre-computed divide.
Honza
>
> -Andi
>
> --
> a...@linux.intel.com -- Speaking for myself only
