From 42bec35f65813fa9fc287edd80314ec64f9fe41f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Gardou?= <jerome.gardou@reactos.org>
Date: Fri, 25 Jun 2021 10:24:04 +0200
Subject: [PATCH] [NTOS:KE] Also rewrite KeZeroPages in assembly for amd64

Let's stick with "rep movsq" until we are able to have more precise benchmarks
---
 ntoskrnl/ke/amd64/stubs.c    | 10 --------
 ntoskrnl/ke/amd64/zeropage.S | 45 ++++++++++++++++++++++++++++++++++++
 ntoskrnl/ntos.cmake          |  3 ++-
 3 files changed, 47 insertions(+), 11 deletions(-)
 create mode 100644 ntoskrnl/ke/amd64/zeropage.S

diff --git a/ntoskrnl/ke/amd64/stubs.c b/ntoskrnl/ke/amd64/stubs.c
index 0683ce73aa4..7aa5866b978 100644
--- a/ntoskrnl/ke/amd64/stubs.c
+++ b/ntoskrnl/ke/amd64/stubs.c
@@ -88,16 +88,6 @@ KiDpcInterruptHandler(VOID)
     KeLowerIrql(OldIrql);
 }
 
-
-VOID
-FASTCALL
-KeZeroPages(IN PVOID Address,
-            IN ULONG Size)
-{
-    /* Not using XMMI in this routine */
-    RtlZeroMemory(Address, Size);
-}
-
 PVOID
 KiSwitchKernelStackHelper(
     LONG_PTR StackOffset,
diff --git a/ntoskrnl/ke/amd64/zeropage.S b/ntoskrnl/ke/amd64/zeropage.S
new file mode 100644
index 00000000000..c663efe04b5
--- /dev/null
+++ b/ntoskrnl/ke/amd64/zeropage.S
@@ -0,0 +1,45 @@
+/*
+ * PROJECT:     ReactOS Kernel
+ * LICENSE:     GPL-2.0-or-later (https://spdx.org/licenses/GPL-2.0-or-later)
+ * PURPOSE:     Fast zeroing of pages
+ * COPYRIGHT:   Copyright 2021 Jérôme Gardou <jerome.gardou@reactos.org>
+ */
+
+#include <asm.inc>
+
+/* FUNCTIONS ****************************************************************/
+.code
+
+/* Benchmarking from Timo on some AMD machine:
+    rep movsq : 128
+    movaps 175
+    movnti 620
+    movntdq: 620
+    movntps: 620
+    MS KeZeroPages (movnti unrolled): 883
+    MS KeZeroSinglePage (mov): 346
+
+    whole discussion in https://github.com/reactos/reactos/pull/3765
+    We stick with rep stosq.
+*/
+
+/*
+ * VOID
+ * KeZeroPages(PVOID Ptr, ULONG Size);
+ */
+PUBLIC KeZeroPages
+FUNC KeZeroPages
+    push rdi
+    .PUSHREG rdi
+    .ENDPROLOG
+
+    mov rdi, rcx
+    mov ecx, edx
+    shr ecx, 3
+    xor rax, rax
+    rep stosq
+    pop rdi
+    ret
+ENDFUNC
+
+END
diff --git a/ntoskrnl/ntos.cmake b/ntoskrnl/ntos.cmake
index 7803e4c812e..50e965f610a 100644
--- a/ntoskrnl/ntos.cmake
+++ b/ntoskrnl/ntos.cmake
@@ -328,7 +328,8 @@ elseif(ARCH STREQUAL "amd64")
         ${REACTOS_SOURCE_DIR}/ntoskrnl/ke/amd64/boot.S
         ${REACTOS_SOURCE_DIR}/ntoskrnl/ke/amd64/ctxswitch.S
         ${REACTOS_SOURCE_DIR}/ntoskrnl/ke/amd64/trap.S
-        ${REACTOS_SOURCE_DIR}/ntoskrnl/ke/amd64/usercall_asm.S)
+        ${REACTOS_SOURCE_DIR}/ntoskrnl/ke/amd64/usercall_asm.S
+        ${REACTOS_SOURCE_DIR}/ntoskrnl/ke/amd64/zeropage.S)
     list(APPEND SOURCE
         ${REACTOS_SOURCE_DIR}/ntoskrnl/config/i386/cmhardwr.c
         ${REACTOS_SOURCE_DIR}/ntoskrnl/mm/i386/page.c