[PATCH] uml: TLB operation batching

This adds VM op batching to skas0.  Rather than having a context switch to and
from the userspace stub for each address space change, we write a number of
operations to the stub data page and invoke a different stub which loops over
them and executes them all in one go.

The operations are stored as [ system call number, arg1, arg2, ... ] tuples.

The set is terminated by a system call number of 0.  Single operations, i.e.
page faults, are handled in the old way, since that is slightly more
efficient.

For a kernel build, a minority (~1/4) of the operations are part of a set.
These sets averaged ~100 in length, so for this quarter, the context switching
overhead is greatly reduced.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/sys-i386/stub.S

@@ -6,3 +6,20 @@ syscall_stub:
 	int 	$0x80
 	mov	%eax, UML_CONFIG_STUB_DATA
 	int3
+
+	.globl batch_syscall_stub
+batch_syscall_stub:
+	mov	$UML_CONFIG_STUB_DATA, %esp
+again:	pop	%eax
+	cmpl	$0, %eax
+	jz	done
+	pop	%ebx
+	pop	%ecx
+	pop	%edx
+	pop	%esi
+ 	pop	%edi
+	pop	%ebp
+	int	$0x80
+	mov	%eax, UML_CONFIG_STUB_DATA
+	jmp	again
+done:	int3