Open lemire opened 2 months ago
Thanks for posting on the panama-dev channel, I'll be following the discussion
Thanks for posting on the panama-dev channel, I'll be following the discussion
I encourage you to chime in. If I am the only voice, I might not carry enough weight.
Just try to hack your code and I bet you will soon find that selectFrom
carry a significant penalty.
They are more likely to listen to people who have been actively trying to use the Vector API.
BTW I ported the algorithm to C#, I am about the make it public. The .NET library has already a very fast UTF-8 validation function (it is internal but we can get at it with copy-paste). As you can see, I get about 25 GB/s per second on Twitter.json. It wasn't more difficult that the work you did.
On an Intel Ice Lake system...
data set | AVX2 (GB/s) | .NET speed (GB/s) |
---|---|---|
Twitter.json | 24 | 12 |
Arabic-Lipsum | 9.0 | 2.3 |
Chinese-Lipsum | 9.0 | 3.9 |
Emoji-Lipsum | 7.1 | 0.9 |
Hebrew-Lipsum | 8.0 | 2.3 |
Hindi-Lipsum | 8.0 | 2.1 |
Japanese-Lipsum | 8.0 | 3.5 |
Korean-Lipsum | 8.0 | 1.3 |
Latin-Lipsum | 76 | 96 |
Russian-Lipsum | 8.0 | 1.2 |
On an Apple M2 system...
data set | ARM NEON (GB/s) | .NET speed (GB/s) |
---|---|---|
Twitter.json | 25 | 14 |
Arabic-Lipsum | 7.4 | 3.5 |
Chinese-Lipsum | 7.4 | 4.8 |
Emoji-Lipsum | 7.4 | 2.5 |
Hebrew-Lipsum | 7.4 | 3.5 |
Hindi-Lipsum | 7.3 | 3.0 |
Japanese-Lipsum | 7.3 | 4.6 |
Korean-Lipsum | 7.4 | 1.8 |
Latin-Lipsum | 87 | 38 |
Russian-Lipsum | 7.4 | 2.7 |
This Java code can be 'fast' but not nearly at the speed of a C implementation.
I believe that the reason is this code section:
At a glance,
selectFrom
looks like a standard vectorized table lookup likevpshufb
orvtbl
. But I think it is not, unfortunately. It appears to generate a long flow of instructions.So the people working on the Java Vector API appear to have assumed that instructions like
vpshufb
orvtbl
were of secondary importance and did not need to be exposed to the programmer. I believe that it is a mistake.The C# approach is quite different. In .NET 8, you have
Ssse3.Shuffle
orAdvSimd.Arm64.VectorTableLookup
for example.See https://mail.openjdk.org/pipermail/panama-dev/2024-June/020476.html