rmuir commented on a change in pull request #69:
URL: https://github.com/apache/lucene/pull/69#discussion_r609185490
##########
File path: lucene/core/src/java/org/apache/lucene/codecs/lucene90/PForUtil.java
##########
@@ -121,4 +167,146 @@ void skip(DataInput in) throws IOException {
in.skipBytes(forUtil.numBytes(bitsPerValue) + (numExceptions << 1));
}
}
+
+ /**
+ * Fill {@code longs} with the final values for the case of all deltas being
1. Note this assumes
+ * there are no exceptions to apply.
+ */
+ private static void prefixSumOfOnes(long[] longs, long base) {
+ System.arraycopy(IDENTITY_PLUS_ONE, 0, longs, 0, ForUtil.BLOCK_SIZE);
+ // This loop gets auto-vectorized
+ for (int i = 0; i < ForUtil.BLOCK_SIZE; ++i) {
+ longs[i] += base;
+ }
+ }
+
+ /**
+ * Fill {@code longs} with the final values for the case of all deltas being
{@code val}. Note
+ * this assumes there are no exceptions to apply.
+ */
+ private static void prefixSumOf(long[] longs, long base, long val) {
+ for (int i = 0; i < ForUtil.BLOCK_SIZE; i++) {
+ longs[i] = (i + 1) * val + base;
Review comment:
> I came across this
[read](http://psy-lob-saw.blogspot.com/2015/07/jmh-perfasm.html) that seemed to
indicate the need to run on "real hardware."
I dont know about this. For me it works fine both on real hardware and
inside QEMU vm, i see similar results for a simple test command passing the
same arguments that jmh does behind the scenes:
```
perf record --freq 1000 --event cycles,instructions --output test.tmp dd
if=/dev/urandom of=/dev/null bs=1M count=100
```
If it says 0 samples, then something is off.
hardware wise, I see the following config:
```
host$ journalctl -k | grep PMU
kernel: Performance Events: PEBS fmt3+, Skylake events, 32-deep LBR,
full-width counters, Intel PMU driver.
guest$ journalctl -k | grep PMU
kernel: Performance Events: Skylake events, full-width counters, Intel PMU
driver.
```
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