rmuir commented on PR #12311:
URL: https://github.com/apache/lucene/pull/12311#issuecomment-1560207056
This isn't a theoretical issue, I really think its a openjdk problem?
To reproduce it, i simply emulate a Nehalem cpu (the one right before AVX):
```
processor : 3
vendor_id : GenuineIntel
cpu family : 6
model : 26
model name : Intel Core i7 9xx (Nehalem Class Core i7)
stepping : 3
microcode : 0x1
cpu MHz : 2496.002
cache size : 16384 KB
physical id : 0
siblings : 4
core id : 1
cpu cores : 2
apicid : 3
initial apicid : 3
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc
rep_good nopl xtopology cpuid tsc_known_freq pni ssse3 cx16 sse4_1 sse4_2
x2apic popcnt hypervisor lahf_lm cpuid_fault
bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds
swapgs itlb_multihit mmio_unknown
bogomips : 4994.00
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:
```
Here's my QEMU command:
```
qemu-system-x86_64 \
-name "Arch Linux" \
-machine q35,vmport=off \
-accel kvm,kernel-irqchip=on \
-cpu Nehalem-v1 \
-smp 4,cores=2,threads=2 \
-m 8192 \
-boot menu=on \
-nodefaults \
-no-user-config \
-object rng-random,id=rng0,filename=/dev/urandom -device
virtio-rng-pci,rng=rng0 \
-nic user,ipv6=off,model=virtio-net-pci,hostfwd=tcp::10022-:22 \
-device virtio-scsi-pci,id=scsi0 \
-device scsi-hd,bus=scsi0.0,drive=drive-scsi0 \
-drive file=disk.qcow2,if=none,id=drive-scsi0,discard=on \
-nographic \
-vga none \
-device virtio-serial-pci \
-device virtserialport \
-device virtconsole \
-serial mon:stdio \
-parallel none
```
Here are benchmark results. It behaves the same as passing `-XX:UseAVX=0` on
the host machine.
```
Benchmark (size) Mode Cnt Score Error
Units
BinaryCosineBenchmark.cosineDistanceNew 1024 thrpt 5 0.010 ± 0.003
ops/us
BinaryCosineBenchmark.cosineDistanceOld 1024 thrpt 5 0.776 ± 0.107
ops/us
BinaryDotProductBenchmark.dotProductNew 1024 thrpt 5 0.023 ± 0.006
ops/us
BinaryDotProductBenchmark.dotProductOld 1024 thrpt 5 1.861 ± 0.087
ops/us
BinarySquareBenchmark.squareDistanceNew 1024 thrpt 5 0.025 ± 0.001
ops/us
BinarySquareBenchmark.squareDistanceOld 1024 thrpt 5 1.555 ± 0.048
ops/us
FloatCosineBenchmark.cosineNew 1024 thrpt 5 3.416 ± 0.256
ops/us
FloatCosineBenchmark.cosineOld 1024 thrpt 5 0.694 ± 0.117
ops/us
FloatDotProductBenchmark.dotProductNew 1024 thrpt 5 8.968 ± 0.125
ops/us
FloatDotProductBenchmark.dotProductOld 1024 thrpt 5 1.835 ± 0.162
ops/us
FloatSquareBenchmark.squareNew 1024 thrpt 5 6.665 ± 0.068
ops/us
FloatSquareBenchmark.squareOld 1024 thrpt 5 1.224 ± 0.151
ops/us
```
```
dev0:vectorbench[main]$ /usr/lib/jvm/java-20-openjdk/bin/jshell
--add-modules jdk.incubator.vector
May 23, 2023 6:24:14 PM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
| Welcome to JShell -- Version 20.0.1
| For an introduction type: /help intro
jshell> jdk.incubator.vector.IntVector.SPECIES_PREFERRED
$1 ==> Species[int, 4, S_128_BIT]
```
128-bit vectors are claimed but don't work. This is not good.
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