From b43108b32586d85d3dca9cb5f5ce76307268c2fb Mon Sep 17 00:00:00 2001
From: divya2108 <divya.kotadiya@fujitsu.com>
Date: Thu, 3 Oct 2024 14:24:00 +0530
Subject: [PATCH] Optimised code design and handled ci test failures

---
 cmake/CheckSVEsupport.cmake |  2 +-
 src/common/hist_util.cc     | 70 ++++++++++++++++++++++---------------
 2 files changed, 43 insertions(+), 29 deletions(-)

diff --git a/cmake/CheckSVEsupport.cmake b/cmake/CheckSVEsupport.cmake
index f7d92ad5f679..3abc19e6b1b2 100644
--- a/cmake/CheckSVEsupport.cmake
+++ b/cmake/CheckSVEsupport.cmake
@@ -1,7 +1,7 @@
 function(check_xgboost_sve_support)
 if(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64")
     include(CheckCSourceCompiles)
-    
+
     # Save the original C_FLAGS to restore later
     set(ORIGINAL_C_FLAGS "${CMAKE_C_FLAGS}")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=armv8-a+sve")
diff --git a/src/common/hist_util.cc b/src/common/hist_util.cc
index 6ee073523f9d..1986a7e4277f 100644
--- a/src/common/hist_util.cc
+++ b/src/common/hist_util.cc
@@ -18,6 +18,7 @@
 
 #ifdef __linux__
 #include <sys/prctl.h>
+#define PR_SVE_GET_VL 51
 #endif
 
 #ifdef XGBOOST_SVE_COMPILER_SUPPORT
@@ -201,7 +202,8 @@ inline void UpdateHistogramWithSVE(size_t row_size, const BinIdxType *gr_index_l
   for (size_t j = 0; j < row_size; j += svcntw()) {
     // Create a predicate (mask) for 32-bit & 64-bit elements, active only for valid elements
     svbool_t pg32 = svwhilelt_b32(j, row_size);
-    svbool_t pg64 = svwhilelt_b64(j, row_size);
+    svbool_t pg64_lower = svwhilelt_b64(j, row_size);
+    svbool_t pg64_upper = svwhilelt_b64(j+svcntd(), row_size);
 
     // Load the gradient index values and offsets for the current chunk of the row
     svuint32_t gr_index_vec =
@@ -216,42 +218,53 @@ inline void UpdateHistogramWithSVE(size_t row_size, const BinIdxType *gr_index_l
       idx_bin_vec = svmul_n_u32_x(pg32, temp, two);
     }
 
-    // Unpack the 32-bit index binary vector into 64-bit vectors from lower and upper half
-    // respectively
+    // Unpack 32-bit index binary vector into 64-bit vectors from lower & upper half respectively
     svuint64_t idx_bin_vec0_0 = svunpklo_u64(idx_bin_vec);
     svuint64_t idx_bin_vec0_1 = svunpkhi_u64(idx_bin_vec);
 
     // Increment the indices by 1 for hessian.
-    svuint64_t idx_bin_vec1_0 = svadd_n_u64_m(pg64, idx_bin_vec0_0, 1);
-    svuint64_t idx_bin_vec1_1 = svadd_n_u64_m(pg64, idx_bin_vec0_1, 1);
+    svuint64_t idx_bin_vec1_0 = svadd_n_u64_m(pg64_lower, idx_bin_vec0_0, 1);
+    svuint64_t idx_bin_vec1_1 = svadd_n_u64_m(pg64_upper, idx_bin_vec0_1, 1);
 
     // Gather the histogram data corresponding to the computed indices
-    svfloat64_t hist0_vec0 = svld1_gather_index(pg64, hist_data, idx_bin_vec0_0);
-    svfloat64_t hist0_vec1 = svld1_gather_index(pg64, hist_data, idx_bin_vec0_1);
-    svfloat64_t hist1_vec0 = svld1_gather_index(pg64, hist_data, idx_bin_vec1_0);
-    svfloat64_t hist1_vec1 = svld1_gather_index(pg64, hist_data, idx_bin_vec1_1);
+    svfloat64_t hist0_vec0 = svld1_gather_index(pg64_lower, hist_data, idx_bin_vec0_0);
+    svfloat64_t hist0_vec1 = svld1_gather_index(pg64_upper, hist_data, idx_bin_vec0_1);
+    svfloat64_t hist1_vec0 = svld1_gather_index(pg64_lower, hist_data, idx_bin_vec1_0);
+    svfloat64_t hist1_vec1 = svld1_gather_index(pg64_upper, hist_data, idx_bin_vec1_1);
 
     // Accumulate the gradient and hessian values into the histogram
-    hist0_vec0 = svadd_f64_m(pg64, hist0_vec0, grad);
-    hist0_vec1 = svadd_f64_m(pg64, hist0_vec1, grad);
-    hist1_vec0 = svadd_f64_m(pg64, hist1_vec0, hess);
-    hist1_vec1 = svadd_f64_m(pg64, hist1_vec1, hess);
+    hist0_vec0 = svadd_f64_m(pg64_lower, hist0_vec0, grad);
+    hist0_vec1 = svadd_f64_m(pg64_upper, hist0_vec1, grad);
+    hist1_vec0 = svadd_f64_m(pg64_lower, hist1_vec0, hess);
+    hist1_vec1 = svadd_f64_m(pg64_upper, hist1_vec1, hess);
 
     // Store the updated histogram data back into memory
-    svst1_scatter_index(pg64, hist_data, idx_bin_vec0_0, hist0_vec0);
-    svst1_scatter_index(pg64, hist_data, idx_bin_vec0_1, hist0_vec1);
-    svst1_scatter_index(pg64, hist_data, idx_bin_vec1_0, hist1_vec0);
-    svst1_scatter_index(pg64, hist_data, idx_bin_vec1_1, hist1_vec1);
+    svst1_scatter_index(pg64_lower, hist_data, idx_bin_vec0_0, hist0_vec0);
+    svst1_scatter_index(pg64_upper, hist_data, idx_bin_vec0_1, hist0_vec1);
+    svst1_scatter_index(pg64_lower, hist_data, idx_bin_vec1_0, hist1_vec0);
+    svst1_scatter_index(pg64_upper, hist_data, idx_bin_vec1_1, hist1_vec1);
   }
 }
 #endif
 
-// Returns true if SVE ISA is available on the current CPU
-bool check_sve_hw_support() {
-  int ret = prctl(PR_SVE_GET_VL);
-  return ret >= 0 ? 1 : 0;
+// Returns true if SVE ISA is available on the current CPU (with caching)
+#ifdef __linux__
+int check_sve_hw_support() {
+    static int cached_sve_support = -1;
+    if (cached_sve_support == -1) {
+        int ret = prctl(PR_SVE_GET_VL);
+        if (ret == -1) {
+            cached_sve_support = 0;
+        } else {
+            cached_sve_support = 1;
+        }
+    }
+    return cached_sve_support;
 }
 
+static int sve_enabled = check_sve_hw_support();
+#endif
+
 template <bool do_prefetch, class BuildingManager>
 void RowsWiseBuildHistKernel(Span<GradientPair const> gpair, Span<bst_idx_t const> row_indices,
                              const GHistIndexMatrix &gmat, GHistRow hist) {
@@ -289,7 +302,6 @@ void RowsWiseBuildHistKernel(Span<GradientPair const> gpair, Span<bst_idx_t cons
                           // 2 FP values: gradient and hessian.
                           // So we need to multiply each row-index/bin-index by 2
                           // to work with gradient pairs as a singe row FP array
-
   for (std::size_t i = 0; i < size; ++i) {
     const size_t icol_start = kAnyMissing ? get_row_ptr(rid[i]) : get_rid(rid[i]) * n_features;
     const size_t icol_end = kAnyMissing ? get_row_ptr(rid[i] + 1) : icol_start + n_features;
@@ -313,12 +325,12 @@ void RowsWiseBuildHistKernel(Span<GradientPair const> gpair, Span<bst_idx_t cons
     }
     const BinIdxType *gr_index_local = gradient_index + icol_start;
 
-    if (check_sve_hw_support()) {
-      #ifdef XGBOOST_SVE_COMPILER_SUPPORT
+    #ifdef XGBOOST_SVE_COMPILER_SUPPORT
+      if (sve_enabled) {
         UpdateHistogramWithSVE(row_size, gr_index_local, offsets, hist_data, p_gpair, idx_gh, two,
-                                kAnyMissing);
-      #endif
-    } else {
+                        kAnyMissing);
+      } else {
+    #endif
         // The trick with pgh_t buffer helps the compiler to generate faster binary.
         const float pgh_t[] = {p_gpair[idx_gh], p_gpair[idx_gh + 1]};
         for (size_t j = 0; j < row_size; ++j) {
@@ -328,7 +340,9 @@ void RowsWiseBuildHistKernel(Span<GradientPair const> gpair, Span<bst_idx_t cons
           *(hist_local) += pgh_t[0];
           *(hist_local + 1) += pgh_t[1];
         }
-    }
+    #ifdef XGBOOST_SVE_COMPILER_SUPPORT
+      }
+    #endif
   }
 }