[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, 21 insertions, 0 deletions

diff --git a/arch/um/sys-x86_64/stub.S b/arch/um/sys-x86_64/stub.S
index 31c14925716b..957f2eff32ca 100644
--- a/arch/um/sys-x86_64/stub.S
+++ b/arch/um/sys-x86_64/stub.S
@@ -13,3 +13,24 @@ syscall_stub:
         or      %rcx, %rbx
         movq    %rax, (%rbx)
         int3
+
+        .globl batch_syscall_stub
+batch_syscall_stub:
+        movq    $(UML_CONFIG_STUB_DATA >> 32), %rbx
+        salq    $32, %rbx
+        movq    $(UML_CONFIG_STUB_DATA & 0xffffffff), %rcx
+        or      %rcx, %rbx
+        movq    %rbx, %rsp
+again:  pop     %rax
+        cmpq    $0, %rax
+jz      done
+        pop     %rdi
+        pop     %rsi
+        pop     %rdx
+        pop     %r10
+        pop     %r8
+        pop     %r9
+        syscall
+        mov     %rax, (%rbx)
+        jmp     again
+done:   int3