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#apertus IRC Channel Logs

2021/11/30

Timezone: UTC


01:21
fredy330
left the channel
01:55
fredy330
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01:55
danieel
vup: the vectorized code is better than a hand crafted sse/avx inline?
01:57
vup
danieel: well I did not try hand crafted sse / avx, but if you look at the generated code: https://rust.godbolt.org/z/aYKnv8Y5e
01:57
vup
its actually super clean
01:57
vup
and probably very similar to what I would come up with
01:59
danieel
thats nice... can we try if it can do Neon? (like on arm?)
02:05
vup
danieel: yeah it looks like the neon code is super clean aswell: https://rust.godbolt.org/z/64q96aenP
02:06
vup
(even nicer than the avx2 code, but that is expected, as sse/avx does not have a lot of instructions for 8 bit integers, for example shifts are missing, so you first need to convert the 8 bit integers to 16 bit integers)
02:07
danieel
is that just what rust gives? or llvm/gcc can do as well?
02:07
danieel
if this can do both.. then no need to use inline asm :)
02:09
vup
I mean that is what rust gives, but as is uses llvm as backend I would expect similar results for c
02:09
vup
and indeed: https://godbolt.org/z/z8zGsndz3
02:10
vup
the naive c translation produces pretty much the exact same code
02:10
vup
(works for sse/avx aswell)
02:11
vup
gcc produces a more complicated, but still vectorized and atleast for sse/avx similarly performing version
02:11
vup
(did not benchmark the neon version myself yet)
02:12
danieel
well, i am amazed
02:12
vup
In general, I would expect the vectorization for c/c++ to be a lot better even than the one for rust, because rust for example has bounds checking for array accesses, which it first has to figure out how to optimize away
02:14
vup
(otoh rust disallows aliasing of mutable references, so thats one point where its simpler for vectorization, but in c you can of course always use `restrict` to help the compiler)
03:03
Bertl_oO
would be nice to see if 'readable' C code can outperorm the neon remapper ;)
03:03
Bertl_oO
*outperform
06:14
Bertl_oO
off to bed now ... have a good one everyone!
06:14
Bertl_oO
changed nick to: Bertl_zZ
07:51
se6astian
good day
07:52
se6astian
vup: bandwidth.bmp uploaded to https://cloud.apertus.org/index.php/s/NsbF5kD4Yt4SpZg
08:39
se6astian
have you seen https://libre-soc.org ?
11:02
se6astian
https://wiki.apertus.org/index.php/Raw12_viewer documentation created and https://wiki.apertus.org/index.php/RAW12 updated
12:51
Bertl_zZ
changed nick to: Bertl
12:51
Bertl
morning folks!
15:10
Bertl
off for now ... bbl
15:11
Bertl
changed nick to: Bertl_oO
15:50
se6astian
vup/anuejn/Bertl_oO: Do you know why black coloumns feature seems to be commented out in current snap code: https://github.com/apertus-open-source-cinema/axiom-firmware/blob/main/software/sensor_tools/snap/snap.c#L620 ?
15:59
se6astian
seems like it was that way from the beginning? a mistake we never noticed?
16:09
se6astian
pushed fixed
16:09
se6astian
https://github.com/apertus-open-source-cinema/axiom-firmware/commit/9eed0c6943af4b007a207f6aefc94e35af57eef1
16:09
se6astian
tested on beta
16:09
se6astian
seems to be working fine
17:06
vup
yeah libre-soc has been around for some time
17:08
vup
not sure about the black column feature
17:25
vup
Bertl_oO: so this seems to get auto-vectorized: https://paste.niemo.de/raw/ixomuboteq
17:25
vup
but one would have to benchmark it against your handrolled version
17:34
vup
also did you every try just mmaping the file instead of converting line by line and then copying that to the file?
18:02
Bertl_oO
the main idea for the conversion is to use it as a 'filter' in a pipeline, so mmaping is not suitable for this purpose
18:03
Bertl_oO
regardings benchmarking: yes, that would be nice to see, se6astian ^^
18:09
vup
Bertl_oO: hmm what more filters do you envision in the pipeline for snap?
18:28
illwieckz
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19:09
Bertl_oO
not necessarily for snap, the idea here was to use memtool to read/write data from/to memory and to convert it on the fly
19:21
vup
right
20:35
balrog
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balrog
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21:12
illwieckz
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23:34
fredy330
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