[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>

1 files changed, 17 insertions, 0 deletions

diff --git a/arch/um/sys-i386/stub.S b/arch/um/sys-i386/stub.S
index 2f2c70a8f043..a0f9506312d1 100644
--- a/arch/um/sys-i386/stub.S
+++ b/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