On 01/03/17 23:58, Steven Newbury wrote:
On Wed, 2017-03-01 at 12:38 +0200, Eero Tamminen wrote:
Hi,
On 01.03.2017 07:25, Timothy Arceri wrote:
This reduces the cache size for Deus Ex from ~160M to ~30M for
radeonsi.
I'm also seeing the following improvements in minimum fps in the
Shadow of Mordor benchmark:
no-cache: ~10fps
with-cache-no-compression: ~15fps
with-cache-and-compression: ~20fps
Note the with cache results are from the second run after closing
and opening the game to avoid the in-memory cache.
Since we only really care about decompression I went with
Z_BEST_COMPRESSION as suggested on irc by Steinar H. Gunderson
who has benchmarked decompression speeds.
Did he tried liblzo instead of zlib?
It should be faster than zlib while still having fairly OK
compression
ratio.
lz4hc would be perfect. Decent compression ratio and very fast
decompression.
So here are my current thoughts:
1) Do we care about fast compression/decompression?
Yes. However there is no indication that zlib is not already fast
enough. The max size I've come across for a cache entry so far is ~200KB
(most are smaller), at this size I'm not sure how useful a faster
implementation is going to be at either compression or decompression.
If anyone has numbers for compression/decompression small files I would
be interested to see them, but since there is currently no obvious
performance bottlenecks it's not on my todo list to make such a
comparison myself.
2) Do were care about compression ratio?
Yes. We currently have a default 1GB limit for the cache (users can
override this). As well as games like Deus Ex having a large footprint,
the Dolphin devs have reported reaching multiple GBs (uncompressed) in a
few hours of running.
Initial testing also seems to point to smaller file sizes increasing
performance due to reduced I/O. More thorough testing is probably needed
to confirm this.
3) Is zlib the best implementation to use?
Maybe not, but we need a baseline for any comparisons. Based on my
testing it seems to do a good job, and addresses a number of issues
raised in 2) compared with no compression.
IMO we should go with zlib and people can provide future patches with
justifications/stats for using a different library over zlib just like
we do for any other performance based patch.
We may even end up with different options. vc4 for example might indeed
be more concerned with (de)compression speed over file size who knows.
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