[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, 4 insertions, 0 deletions

diff --git a/arch/x86_64/ia32/ptrace32.c b/arch/x86_64/ia32/ptrace32.c
index 659c0722f6b8..72bf92a9d375 100644
--- a/arch/x86_64/ia32/ptrace32.c
+++ b/arch/x86_64/ia32/ptrace32.c
@@ -117,6 +117,10 @@ static int putreg32(struct task_struct *child, unsigned regno, u32 val)
                         if ((0x5454 >> ((val >> (16 + 4*i)) & 0xf)) & 1)
                                return -EIO;
                 child->thread.debugreg7 = val; 
+                if (val)
+                        set_tsk_thread_flag(child, TIF_DEBUG);
+                else
+                        clear_tsk_thread_flag(child, TIF_DEBUG);
                 break; 
                     
         default: