[NTOS]: Optimize new context switching code to avoid wasted cycles.

svn path=/trunk/; revision=49523

reactos/ntoskrnl/include/internal/ke.h

@@ -298,8 +298,8 @@ KeReadStateThread(IN PKTHREAD Thread);
 BOOLEAN
 FASTCALL
 KiSwapContext(
-    IN PKTHREAD CurrentThread,
+    IN KIRQL WaitIrql,
-    IN PKTHREAD NewThread
+    IN PKTHREAD CurrentThread
 );
 
 VOID

reactos/ntoskrnl/ke/dpc.c

@@ -534,7 +534,7 @@ KiQuantumEnd(VOID)
     Thread->WaitIrql = APC_LEVEL;
 
     /* Swap threads */
-    KiSwapContext(Thread, NextThread);
+    KiSwapContext(APC_LEVEL, Thread);
 
     /* Lower IRQL back to DISPATCH_LEVEL */
     KeLowerIrql(DISPATCH_LEVEL);

reactos/ntoskrnl/ke/i386/ctxswitch.S

@@ -13,70 +13,20 @@
 #include <ndk/asm.h>
 .intel_syntax noprefix
 
-#define Ready 1
-#define Running 2
-#define WrDispatchInt 0x1F
-
 /* FUNCTIONS ****************************************************************/
 
-/*++
- * KiSwapContextInternal 
- *
- *     The KiSwapContextInternal routine switches context to another thread.
- *
- * Params:
- *     ESI - Pointer to the KTHREAD to which the caller wishes to
- *           switch to.
- *     EDI - Pointer to the KTHREAD to which the caller wishes to
- *           switch from.
- *
- * Returns:
- *     None.
- *
- * Remarks:
- *     Absolutely all registers except ESP can be trampled here for maximum code flexibility.
- *
- *--*/
 .globl @KiSwapContextInternal@0
 .func @KiSwapContextInternal@0, @KiSwapContextInternal@0
 @KiSwapContextInternal@0:
-    /* Set APC Bypass Disable and old thread pointer */
-    mov edx, edi
-    or dl, cl
-
     /* Build switch frame */
     sub esp, 2 * 4
     mov ecx, esp
-    call @KiSwapContextEntry@8
+    jmp @KiSwapContextEntry@8
-    mov ecx, 0xB00BFACA
-    jmp $
 .endfunc
 
-/*++
- * KiSwapContext 
- *
- *     The KiSwapContext routine switches context to another thread.
- *
- * Params:
- *     TargetThread - Pointer to the KTHREAD to which the caller wishes to
- *                    switch to.
- *
- * Returns:
- *     The WaitStatus of the Target Thread.
- *
- * Remarks:
- *     This is a wrapper around KiSwapContextInternal which will save all the
- *     non-volatile registers so that the Internal function can use all of
- *     them. It will also save the old current thread and set the new one.
- *
- *     The calling thread does not return after KiSwapContextInternal until 
- *     another thread switches to IT.
- *
- *--*/
 .globl @KiSwapContext@8
 .func @KiSwapContext@8, @KiSwapContext@8
 @KiSwapContext@8:
-
     /* Save 4 registers */
     sub esp, 4 * 4
 
@@ -86,17 +36,8 @@
     mov [esp+4], edi
     mov [esp+0], ebp
 
-    /* Get the current KPCR */
-    mov ebx, fs:[KPCR_SELF]
-
-    /* Get the Current Thread */
-    mov edi, ecx
-
-    /* Get the New Thread */
-    mov esi, edx
-
     /* Get the wait IRQL */
-    movzx ecx, byte ptr [edi+KTHREAD_WAIT_IRQL]
+    or dl, cl
 
     /* Do the swap with the registers correctly setup */
     call @KiSwapContextInternal@0
@@ -112,10 +53,21 @@
     ret
 .endfunc
 
+.globl @KiSwitchThreads@8
+.func @KiSwitchThreads@8, @KiSwitchThreads@8
+@KiSwitchThreads@8:
+    /* Load the new kernel stack and switch OS to new thread */
+    mov esp, edx
+    call @KiSwapContextExit@8
+    
+    /* Now we're on the new thread. Return to the caller to restore registers */
+    add esp, 2 * 4
+    ret
+.endfunc
+
 .globl @KiRetireDpcListInDpcStack@8
 .func @KiRetireDpcListInDpcStack@8, @KiRetireDpcListInDpcStack@8
 @KiRetireDpcListInDpcStack@8:
-
     /* Switch stacks and retire DPCs */
     mov eax, esp
     mov esp, edx
@@ -140,20 +92,6 @@ _Ki386SetupAndExitToV86Mode@4:
     jmp $
 .endfunc
 
-.globl @KiSwitchThreads@8
-.func @KiSwitchThreads@8, @KiSwitchThreads@8
-@KiSwitchThreads@8:
-
-    /* Load the new kernel stack and switch OS to new thread */
-    mov esp, [edx+KTHREAD_KERNEL_STACK]
-    mov edx, esp
-    call @KiSwapContextExit@8
-    
-    /* Now we're on the new thread. Return to the caller to restore registers */
-    add esp, 2 * 4
-    ret
-.endfunc
-
 .globl @Ki386BiosCallReturnAddress@4
 @Ki386BiosCallReturnAddress@4:
 

reactos/ntoskrnl/ke/i386/thrdini.c

@@ -309,7 +309,7 @@ KiIdleLoop(VOID)
             NewThread->State = Running;
         
             /* Switch away from the idle thread */
-            KiSwapContext(OldThread, NewThread);
+            KiSwapContext(APC_LEVEL, OldThread);
             
             /* We are back in the idle thread -- disable interrupts again */
             _enable();
@@ -416,9 +416,6 @@ KiSwapContextEntry(IN PKSWITCHFRAME SwitchFrame,
     PKTHREAD OldThread, NewThread;
     ULONG Cr0, NewCr0;
 
-    /* Switch threads, check for APC disable */
-    ASSERT(OldThreadAndApcFlag &~ 1);
-
     /* Save APC bypass disable */
     SwitchFrame->ApcBypassDisable = OldThreadAndApcFlag & 3;
     SwitchFrame->ExceptionList = Pcr->NtTib.ExceptionList;
@@ -451,7 +448,7 @@ KiSwapContextEntry(IN PKSWITCHFRAME SwitchFrame,
 
     /* Now enable interrupts and do the switch */
     _enable();
-    KiSwitchThreads(OldThread, NewThread);
+    KiSwitchThreads(OldThread, NewThread->KernelStack);
 }
 
 VOID
@@ -509,8 +506,8 @@ KiDispatchInterrupt(VOID)
         /* Make the old thread ready */
         KxQueueReadyThread(OldThread, Prcb);
         
-        /* Swap to the new thread. FIXME: APC Bypass */
+        /* Swap to the new thread */
-        KiSwapContext(OldThread, NewThread);
+        KiSwapContext(APC_LEVEL, OldThread);
     }
 }
 

reactos/ntoskrnl/ke/thrdschd.c

@@ -387,7 +387,7 @@ KiSwapThread(IN PKTHREAD CurrentThread,
     WaitIrql = CurrentThread->WaitIrql;
 
     /* Swap contexts */
-    ApcState = KiSwapContext(CurrentThread, NextThread);
+    ApcState = KiSwapContext(WaitIrql, CurrentThread);
 
     /* Get the wait status */
     WaitStatus = CurrentThread->WaitStatus;
@@ -754,7 +754,7 @@ NtYieldExecution(VOID)
             ASSERT(OldIrql <= DISPATCH_LEVEL);
 
             /* Swap to new thread */
-            KiSwapContext(Thread, NextThread);
+            KiSwapContext(APC_LEVEL, Thread);
             Status = STATUS_SUCCESS;
         }
         else

reactos/ntoskrnl/ke/wait.c

@@ -249,7 +249,7 @@ KiExitDispatcher(IN KIRQL OldIrql)
     Thread->WaitIrql = OldIrql;
 
     /* Swap threads and check if APCs were pending */
-    PendingApc = KiSwapContext(Thread, NextThread);
+    PendingApc = KiSwapContext(OldIrql, Thread);
     if (PendingApc)
     {
         /* Lower only to APC */