[Mesa-dev] [PATCH 0/4] RFC: Quadratic probing for the win

[Timothy Arceri]

On Wed, 2017-02-08 at 15:59 -0800, Jason Ekstrand wrote:
> On Wed, Feb 8, 2017 at 3:01 PM, Marek Olšák <maraeo at gmail.com> wrote:
> > I think this is good stuff. I'd gladly take it just for the shader-
> > db
> > improvement.
> > 
> 
> Agreed.  If it really did hurt minecraft before, we should try that
> again just to be sure, but I like faster shader compilation.

Maybe someone should do a quick test with a larger shader-db
collection. Not that the results don't look good but I believe Thomas
has a smaller collection that the one used by Marek and Intel.


>  
> > Marek
> > 
> > On Wed, Feb 8, 2017 at 11:35 PM, Thomas Helland
> > <thomashelland90 at gmail.com> wrote:
> > > 2017-02-08 22:07 GMT+01:00 Thomas Helland <thomashelland90 at gmail.
> > com>:
> > >> 2017-02-08 21:35 GMT+01:00 Thomas Helland <thomashelland90 at gmail
> > .com>:
> > >>> I was cleaning up my local git repo, and came across this
> > series.
> > >>> Last time it was discussed was all the way back in April 2015.
> > >>> Things looked pretty good back then, but we where seeing a
> > smaller
> > >>> regression in CPU-bound scenarios as Eric found with forcing
> > software
> > >>> rendering while running Minecraft.
> > >>>
> > >>> I figured I'd do a retest of the series to see how it fares
> > today.
> > >>> Using perf on shader-db I see:
> > >>> hash_table_search being cut from 3.88% down to 1.83%.
> > >>> _mesa_hash_data being cut from 1.47% down to 1.25%
> > >>> _mesa_hash_table_rehash going from 0.23% up to 1.16%
> > >>> hash_table_insert being cut from 2.26% down to 0.33%
> > >>>
> > >>
> > >> This stats are wrong. I recompiled stuff, so the symbols got
> > >> mangled in the libraries. So here is the correct data (after
> > increasing
> > >> the initial size of the set and hash table to 8, so not
> > perfectly comparable):
> > >> hash_table_search: 3.88% -> 1.84%
> > >> hash_table_insert: 2.26% -> 1.16%
> > >> _mesa_hash_data is unchanged (which is kinda obvious).
> > >> set_add: 0.70% -> 0.35%
> > >> set_search: 0.59% -> 0.27%
> > >>
> > >>> This yields an approximate 10% reduction in shader-db runtime.
> > >>>
> > >>> The increase in the rehash function is a bit peculiar.
> > >>> I'll look into increasing the table one more step, as a four
> > entry
> > >>> hash table seems a bit on the low side. I'll also work on
> > getting
> > >>> some more reliable numbers from a real world application, along
> > >>> with some more runs of shader-db to get better statistical
> > certainty.
> > >>> I'll pull out my i3-6100 / RX460 combo and give this a spin
> > >>> with Borderlands 2 I think, as Marek's threaded GL work
> > suggests
> > >>> this is a title with heavy CPU bottlenecking.
> > >>>
> > >
> > > Using this hardware I ran the Metro LL Redux benchmark mode
> > > through phoronix-test-suite as a quick test. Average fps improved
> > > from 43,97 to 45.23. So not insane, but a decent gain of 2-3%.
> > > I'll come back with some more numbers from in-game play of
> > > some other games in my possession. Likely CS:GO, portal,
> > > TF2, dota2, borderlands 2, or some other games I have.
> > >
> > >>> As a side note, Robin Hood hashing was mentioned in the thread
> > from
> > >>> back in April 2015. I actually have an implementation of that,
> > but
> > >>> I'm still working out an issue that our make-check tests
> > doesn't
> > >>> catch that causes corruption in the table when runing shader-
> > db.
> > >>> I'm not to sure about it's effect though, as it sacrifices
> > insert
> > >>> speed for lookup speed, but one never knows until one tests.
> > >>>
> > >>> Let me know if this is something I should persue. If not I'll
> > >>> mark this series as "junk" in my git repo, and get on with the
> > cleaning.
> > >>>
> > >>> Thomas Helland (4):
> > >>>   util/tests: Expand collision test for hash table
> > >>>   util: Change hash_table to use quadratic probing
> > >>>   util: Change util/set to use quadratic probing
> > >>>   util: Use set_foreach instead of rolling our own
> > >>>
> > >>>  src/util/hash_table.c                 | 102 +++++++++---------
> > -----------
> > >>>  src/util/hash_table.h                 |   3 +-
> > >>>  src/util/set.c                        | 118 ++++++++++++----
> > ------------------
> > >>>  src/util/set.h                        |   3 +-
> > >>>  src/util/tests/hash_table/collision.c |  14 ++++
> > >>>  5 files changed, 89 insertions(+), 151 deletions(-)
> > >>>
> > >>> --
> > >>> 2.11.1
> > >>>
> > > _______________________________________________
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> 
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