(systemds) branch main updated: [SYSTEMDS-3896] Improved SIMD Vectorized Counting NNZ

[mboehm7]

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mboehm7 pushed a commit to branch main
in repository https://gitbox.apache.org/repos/asf/systemds.git


The following commit(s) were added to refs/heads/main by this push:
     new 2c737bc1b8 [SYSTEMDS-3896] Improved SIMD Vectorized Counting NNZ
2c737bc1b8 is described below

commit 2c737bc1b894b88eed684ced55c65be1c777aba5
Author: Matthias Boehm <mboe...@gmail.com>
AuthorDate: Wed Jul 16 11:18:27 2025 +0200

    [SYSTEMDS-3896] Improved SIMD Vectorized Counting NNZ
    
    This patch makes an additional performance improvement which further
    reduced the runtime on an 8GB matrix from 850ms to 770ms
    (non-vectorized 1100) by avoiding unnecessary scalar ops. Furthermore,
    we fix the hard-coded AVX512 vector size to the general vector length
    (which failed on non-Intel hardware in gitactions).
---
 src/main/java/org/apache/sysds/runtime/util/UtilFunctions.java | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/main/java/org/apache/sysds/runtime/util/UtilFunctions.java 
b/src/main/java/org/apache/sysds/runtime/util/UtilFunctions.java
index 4f0a15d78f..3fd1dfd1a3 100644
--- a/src/main/java/org/apache/sysds/runtime/util/UtilFunctions.java
+++ b/src/main/java/org/apache/sysds/runtime/util/UtilFunctions.java
@@ -880,15 +880,17 @@ public class UtilFunctions {
        }
        
        public static int computeNnz(final double[] a, final int ai, final int 
len) {
-               int lnnz = 0;
                final int end = ai + len;
                final int rest = (end - ai) % vLen;
+               int lnnz = len;
 
+               //start from len and subtract number of zeros because
+               //DoubleVector defines an eq but no neq operation
                for(int i = ai; i < ai + rest; i++)
-                       lnnz += (a[i] != 0.0) ? 1 : 0;
-               for(int i = ai + rest; i < end; i += 8) {
+                       lnnz -= (a[i] == 0.0) ? 1 : 0;
+               for(int i = ai + rest; i < end; i += vLen) {
                        DoubleVector aVec = DoubleVector.fromArray(SPECIES, a, 
i);
-                       lnnz += vLen-aVec.eq(0).trueCount();
+                       lnnz -= aVec.eq(0).trueCount();
                }
                return lnnz;
        }