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

[Jason Ekstrand]

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.


> 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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