[PATCH] x86-64 TIF flags for debug regs and io bitmap in ctxsw

Hello,

Following my discussion with Andi. Here is a patch that introduces
two new TIF flags to simplify the context switch code in __switch_to().
The idea is to minimize the number of cache lines accessed in the common
case, i.e., when neither the debug registers nor the I/O bitmap are used.

This patch covers the x86-64 modifications. A patch for i386 follows.

Changelog:
	- add TIF_DEBUG to track when debug registers are active
	- add TIF_IO_BITMAP to track when I/O bitmap is used
	- modify __switch_to() to use the new TIF flags

<signed-off-by>: eranian@hpl.hp.com

Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/ioport.c b/arch/x86_64/kernel/ioport.c
index b81614970ecc..fe063d3cfe42 100644
--- a/arch/x86_64/kernel/ioport.c
+++ b/arch/x86_64/kernel/ioport.c
@@ -56,6 +56,7 @@ asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
 
                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
                 t->io_bitmap_ptr = bitmap;
+                set_thread_flag(TIF_IO_BITMAP);
         }
 
         /*