[PATCH for review] [30/145] x86_64: x86-64 TIF flags for debug regs and io bitmap in ctxsw

Andi Kleen
2006-08-10T20:14:29Z

r

From: Stephane Eranian <eranian@hpl.hp.com>
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>

---
arch/x86_64/ia32/ptrace32.c | 4 ++
arch/x86_64/kernel/ioport.c | 1
arch/x86_64/kernel/process.c | 73 ++++++++++++++++++++++-----------------
arch/x86_64/kernel/ptrace.c | 8 +++-
include/asm-x86_64/thread_info.h | 7 +++
5 files changed, 60 insertions(+), 33 deletions(-)

Index: linux/arch/x86_64/ia32/ptrace32.c
===================================================================
--- linux.orig/arch/x86_64/ia32/ptrace32.c
+++ linux/arch/x86_64/ia32/ptrace32.c
@@ -117,6 +117,10 @@ static int putreg32(struct task_struct *
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:
Index: linux/arch/x86_64/kernel/ioport.c
===================================================================
--- linux.orig/arch/x86_64/kernel/ioport.c
+++ linux/arch/x86_64/kernel/ioport.c
@@ -56,6 +56,7 @@ asmlinkage long sys_ioperm(unsigned long

memset(bitmap, 0xff, IO_BITMAP_BYTES);
t->io_bitmap_ptr = bitmap;
+ set_thread_flag(TIF_IO_BITMAP);
}

/*
Index: linux/arch/x86_64/kernel/process.c
===================================================================
--- linux.orig/arch/x86_64/kernel/process.c
+++ linux/arch/x86_64/kernel/process.c
@@ -350,6 +350,7 @@ void exit_thread(void)

kfree(t->io_bitmap_ptr);
t->io_bitmap_ptr = NULL;
+ clear_thread_flag(TIF_IO_BITMAP);
/*
* Careful, clear this in the TSS too:
*/
@@ -369,6 +370,7 @@ void flush_thread(void)
if (t->flags & _TIF_IA32)
current_thread_info()->status |= TS_COMPAT;
}
+ t->flags &= ~_TIF_DEBUG;

tsk->thread.debugreg0 = 0;
tsk->thread.debugreg1 = 0;
@@ -461,7 +463,7 @@ int copy_thread(int nr, unsigned long cl
asm("mov %%es,%0" : "=m" (p->thread.es));
asm("mov %%ds,%0" : "=m" (p->thread.ds));

- if (unlikely(me->thread.io_bitmap_ptr != NULL)) {
+ if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
if (!p->thread.io_bitmap_ptr) {
p->thread.io_bitmap_max = 0;
@@ -469,6 +471,7 @@ int copy_thread(int nr, unsigned long cl
}
memcpy(p->thread.io_bitmap_ptr, me->thread.io_bitmap_ptr,
IO_BITMAP_BYTES);
+ set_tsk_thread_flag(p, TIF_IO_BITMAP);
}

/*
@@ -498,6 +501,40 @@ out:
*/
#define loaddebug(thread,r) set_debugreg(thread->debugreg ## r, r)

+static inline void __switch_to_xtra(struct task_struct *prev_p,
+ struct task_struct *next_p,
+ struct tss_struct *tss)
+{
+ struct thread_struct *prev, *next;
+
+ prev = &prev_p->thread,
+ next = &next_p->thread;
+
+ if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
+ loaddebug(next, 0);
+ loaddebug(next, 1);
+ loaddebug(next, 2);
+ loaddebug(next, 3);
+ /* no 4 and 5 */
+ loaddebug(next, 6);
+ loaddebug(next, 7);
+ }
+
+ if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
+ /*
+ * Copy the relevant range of the IO bitmap.
+ * Normally this is 128 bytes or less:
+ */
+ memcpy(tss->io_bitmap, next->io_bitmap_ptr,
+ max(prev->io_bitmap_max, next->io_bitmap_max));
+ } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
+ /*
+ * Clear any possible leftover bits:
+ */
+ memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
+ }
+}
+
/*
* switch_to(x,y) should switch tasks from x to y.
*
@@ -586,37 +623,11 @@ __switch_to(struct task_struct *prev_p,
task_stack_page(next_p) + THREAD_SIZE - PDA_STACKOFFSET);

/*
- * Now maybe reload the debug registers
+ * Now maybe reload the debug registers and handle I/O bitmaps
*/
- if (unlikely(next->debugreg7)) {
- loaddebug(next, 0);
- loaddebug(next, 1);
- loaddebug(next, 2);
- loaddebug(next, 3);
- /* no 4 and 5 */
- loaddebug(next, 6);
- loaddebug(next, 7);
- }
-
-
- /*
- * Handle the IO bitmap
- */
- if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr)) {
- if (next->io_bitmap_ptr)
- /*
- * Copy the relevant range of the IO bitmap.
- * Normally this is 128 bytes or less:
- */
- memcpy(tss->io_bitmap, next->io_bitmap_ptr,
- max(prev->io_bitmap_max, next->io_bitmap_max));
- else {
- /*
- * Clear any possible leftover bits:
- */
- memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
- }
- }
+ if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
+ || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
+ __switch_to_xtra(prev_p, next_p, tss);

return prev_p;
}
Index: linux/arch/x86_64/kernel/ptrace.c
===================================================================
--- linux.orig/arch/x86_64/kernel/ptrace.c
+++ linux/arch/x86_64/kernel/ptrace.c
@@ -420,9 +420,13 @@ long arch_ptrace(struct task_struct *chi
if ((0x5554 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
break;
if (i == 4) {
- child->thread.debugreg7 = data;
+ child->thread.debugreg7 = data;
+ if (data)
+ set_tsk_thread_flag(child, TIF_DEBUG);
+ else
+ clear_tsk_thread_flag(child, TIF_DEBUG);
ret = 0;
- }
+ }
break;
}
break;
Index: linux/include/asm-x86_64/thread_info.h
===================================================================
--- linux.orig/include/asm-x86_64/thread_info.h
+++ linux/include/asm-x86_64/thread_info.h
@@ -120,6 +120,8 @@ static inline struct thread_info *stack_
#define TIF_FORK 18 /* ret_from_fork */
#define TIF_ABI_PENDING 19
#define TIF_MEMDIE 20
+#define TIF_DEBUG 21 /* uses debug registers */
+#define TIF_IO_BITMAP 22 /* uses I/O bitmap */

#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
@@ -133,6 +135,8 @@ static inline struct thread_info *stack_
#define _TIF_IA32 (1<<TIF_IA32)
#define _TIF_FORK (1<<TIF_FORK)
#define _TIF_ABI_PENDING (1<<TIF_ABI_PENDING)
+#define _TIF_DEBUG (1<<TIF_DEBUG)
+#define _TIF_IO_BITMAP (1<<TIF_IO_BITMAP)

/* work to do on interrupt/exception return */
#define _TIF_WORK_MASK \
@@ -140,6 +144,9 @@ static inline struct thread_info *stack_
/* work to do on any return to user space */
#define _TIF_ALLWORK_MASK (0x0000FFFF & ~_TIF_SECCOMP)

+/* flags to check in __switch_to() */
+#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)
+
#define PREEMPT_ACTIVE 0x10000000

/*