From 6d1edca727fb1b91a6f46a7a863474286be30da0 Mon Sep 17 00:00:00 2001
From: Dipal M Zambare <DipalMadhukar.Zambare@amd.com>
Date: Tue, 1 Feb 2022 10:22:58 +0530
Subject: [PATCH] Optimized CPU feature determination.

We added new API to check if the CPU architecture has support
for AVX instruction. This API was calling CPUID instruction
every time it is invoked. However, since this information does
not change at runtime, it is sufficient to determine it once
and use the cached results for subsequent calls. This optimization
is needed to improve performance for small size matrix vector
operations.

AMD-Internal: [CPUPL-2009]
Change-Id: If6697e1da6dd6b7f28fbfed45215ea3fdd569c5f
---
 frame/base/bli_cpuid.c | 45 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/frame/base/bli_cpuid.c b/frame/base/bli_cpuid.c
index 98ea947f3..dfac51044 100644
--- a/frame/base/bli_cpuid.c
+++ b/frame/base/bli_cpuid.c
@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018-2021, Advanced Micro Devices, Inc. All rights reserved.
+   Copyright (C) 2018-2022, Advanced Micro Devices, Inc. All rights reserved.
    Copyright (C) 2019, Dave Love, University of Manchester
 
    Redistribution and use in source and binary forms, with or without
@@ -501,13 +501,23 @@ bool bli_cpuid_is_bulldozer
 	return TRUE;
 }
 
-bool bli_cpuid_is_avx_supported( void )
+// Check (at runtime) if AVX is supported on the current platform, this is to 
+// ensure that AVX kernels are not used on legacy platforms which results in crash
+
+// The support for AVX is checked only once (when this API is called first time)
+// On subsequent calls the cached value is returned. This is achieved using 
+// pthread_once mechanism since this information does not change once the library
+// is loaded.
+static bool is_avx_supported = FALSE;
+
+
+// Determine if the CPU has support for AVX.
+void bli_cpuid_check_avx_support( void )
 {
 	uint32_t family, model, features;
 
 	// Call the CPUID instruction and parse its results into a family id,
-	// model id, and a feature bit field. The return value encodes the
-	// vendor.
+	// model id, and a feature bit field.
 	bli_cpuid_query( &family, &model, &features );
 
 	// Check for expected CPU features.
@@ -515,9 +525,32 @@ bool bli_cpuid_is_avx_supported( void )
 	                          FEATURE_FMA3    |
 	                          FEATURE_AVX2;
 
-	if ( !bli_cpuid_has_features( features, expected ) ) return FALSE;
+	if ( !bli_cpuid_has_features( features, expected ) ) 
+	{
+		is_avx_supported = FALSE;
+	}
+	else 
+	{
+		is_avx_supported = TRUE;
+	}
+}
 
-	return TRUE;
+static bli_pthread_once_t once_check_avx_support = BLIS_PTHREAD_ONCE_INIT;
+
+// Ensure that actual support determincation happens only once
+void bli_cpuid_check_avx_support_once( void )
+{
+#ifndef BLIS_CONFIGURETIME_CPUID
+	bli_pthread_once( &once_check_avx_support,  bli_cpuid_check_avx_support );
+#endif
+}
+
+// API to check if AVX is supported or not on the current platform.
+bool bli_cpuid_is_avx_supported( void )
+{
+	bli_cpuid_check_avx_support_once();
+
+	return is_avx_supported;
 }
 
 #elif defined(__aarch64__) || defined(__arm__) || defined(_M_ARM)