Use our knowledge that pointers are at least 4 byte aligned to remove
the useless digits. Then shift by 6, 10, and 14 bits and add this to
the original pointer, effectively folding in the entropy of the higher
bits of the pointer into a 4-bit section. Stopping at 14 means we can
add the entropy from 18 bits, or at least a 600Kbyte section of memory.
Assuming that ralloc allocates from a linearly allocated heap less than
this we can make a very efficient pointer hashing function for our usecase.
Even if we are not on an architecture that is 4 byte aligned, there is
still a high big chance that the thing we are allocating is at least
8 bytes in size, so even then we will have entropy into the third bit.
The 4 bit increment on the shifts is chosen rather arbitrarily; if we
had chosen a 3 bit increment we would need to add another xor to
cover a decently sized memorypool. Increasing it to 5 bits would
spread our entropy more, possibly hurting us with more collisions on
hash tables of size less than 32. With a hash table of size 16 there
are a max of 11 entries, and we can assume that with such a small table
collisions are not that painfull.
This allows us to hash the whole 32 or 64 bit pointer at once,
instead of running FNV1a, looping through each byte and doing
increments, decrements, muls, and xors on every byte. This cuts
_mesa_hash_data from 1.5 % on profiles, to making _mesa_hash_pointer
show up with a 0.09% share. Collisions on insertion actually seems to be
ever so slightly lower with this hash function, as found by printing
a loop counter and sorting the data.
perf stat shows a 1.5% reduction in instruction count,
and a 5% reduction in stalled cycles. Shader-db runtime goes
from 225 to 220 seconds.
No instruction-count changes in shader-db, but there are some minor
changes in cycle-count that is likely caused by nir walking a set
in some of its passes, and this causing a different ordering.
That might eventually lead to a difference in register allocation.
However, the effect is a net positive;
total cycles in shared programs: 24739550 -> 24738482 (-0.00%)
cycles in affected programs: 374468 -> 373400 (-0.29%)
helped: 178
HURT: 49
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
It is included through the util/hash_table include in
the program hash_table, so this should be safe.
This will be needed when we start converting each use of
the program_hash_table, as some places need this function.
Signed-off-by: Thomas Helland <thomashelland90@gmail.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
src/util/hash_table.h:111:23: warning: ‘_mesa_fnv32_1a_offset_bias’ defined but not used [-Wunused-const-variable]
static const uint32_t _mesa_fnv32_1a_offset_bias = 2166136261u;
^~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
We already have search_pre_hashed. This makes the APIs match better.
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Previously, the hash_table API required the user to do all of the hashing
of keys as it passed them in. Since the hashing function is intrinsically
tied to the comparison function, it makes sense for the hash table to know
about it. Also, it makes for a somewhat clumsy API as the user is
constantly calling hashing functions many of which have long names. This
is especially bad when the standard call looks something like
_mesa_hash_table_insert(ht, _mesa_pointer_hash(key), key, data);
In the above case, there is no reason why the hash table shouldn't do the
hashing for you. We leave the option for you to do your own hashing if
it's more efficient, but it's no longer needed. Also, if you do do your
own hashing, the hash table will assert that your hash matches what it
expects out of the hashing function. This should make it harder to mess up
your hashing.
v2: change to call the old entrypoint "pre_hashed" rather than
"with_hash", like cworth's equivalent change upstream (change by
anholt, acked-in-general by Jason).
Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
This gathers macros that have been included across components into util so
that the include chain can be more vertical. In particular, this makes
util stand on its own without any dependence whatsoever on the rest of
mesa.
Signed-off-by: "Jason Ekstrand" <jason.ekstrand@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
This hash table is used in core Mesa, the GLSL compiler, and the i965
driver, which makes it a good candidate for the new src/util module.
It's much faster than program/hash_table.[ch] (see commit 6991c2922f
for data), and José's u_hash_table.c has a comment saying Gallium should
probably consider switching to a linear probing hash table at some point.
So this seems like the best candidate for a shared data structure.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
v2 (Jason Ekstrand): Pick up another hash_table use and patch up scons
Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
2014-08-04 11:07:05 -07:00
Renamed from src/mesa/main/hash_table.h (Browse further)
Thomas Helland
Rob Clark
Nicolai Hähnle
Jason Ekstrand
Jason Ekstrand
Brian Paul
Kenneth Graunke