[PATCH] i386: use thread_info flags for debug regs and IO bitmaps

Use thread info flags to track use of debug registers and IO bitmaps.

 - 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

Performance tested on Pentium II, ten runs of LMbench context switch
benchmark (smaller is better:)

	before	after
avg	3.65	3.39
min	3.55	3.33

Signed-off-by: Stephane Eranian <eranian@hpl.hp.com>
Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 29 insertions, 21 deletions

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 94e2c87edeaa..923bb292f47f 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -359,16 +359,16 @@ EXPORT_SYMBOL(kernel_thread);
  */
 void exit_thread(void)
 {
-        struct task_struct *tsk = current;
-        struct thread_struct *t = &tsk->thread;
-
         /* The process may have allocated an io port bitmap... nuke it. */
-        if (unlikely(NULL != t->io_bitmap_ptr)) {
+        if (unlikely(test_thread_flag(TIF_IO_BITMAP))) {
+                struct task_struct *tsk = current;
+                struct thread_struct *t = &tsk->thread;
                 int cpu = get_cpu();
                 struct tss_struct *tss = &per_cpu(init_tss, cpu);
 
                 kfree(t->io_bitmap_ptr);
                 t->io_bitmap_ptr = NULL;
+                clear_thread_flag(TIF_IO_BITMAP);
                 /*
                  * Careful, clear this in the TSS too:
                  */
@@ -387,6 +387,7 @@ void flush_thread(void)
 
         memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
         memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));        
+        clear_tsk_thread_flag(tsk, TIF_DEBUG);
         /*
          * Forget coprocessor state..
          */
@@ -431,7 +432,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
         savesegment(gs,p->thread.gs);
 
         tsk = current;
-        if (unlikely(NULL != tsk->thread.io_bitmap_ptr)) {
+        if (unlikely(test_tsk_thread_flag(tsk, 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;
@@ -439,6 +440,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
                 }
                 memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
                         IO_BITMAP_BYTES);
+                set_tsk_thread_flag(p, TIF_IO_BITMAP);
         }
 
         /*
@@ -533,10 +535,24 @@ int dump_task_regs(struct task_struct *tsk, elf_gregset_t *regs)
         return 1;
 }
 
-static inline void
-handle_io_bitmap(struct thread_struct *next, struct tss_struct *tss)
+static noinline void __switch_to_xtra(struct task_struct *next_p,
+                                    struct tss_struct *tss)
 {
-        if (!next->io_bitmap_ptr) {
+        struct thread_struct *next;
+
+        next = &next_p->thread;
+
+        if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
+                set_debugreg(next->debugreg[0], 0);
+                set_debugreg(next->debugreg[1], 1);
+                set_debugreg(next->debugreg[2], 2);
+                set_debugreg(next->debugreg[3], 3);
+                /* no 4 and 5 */
+                set_debugreg(next->debugreg[6], 6);
+                set_debugreg(next->debugreg[7], 7);
+        }
+
+        if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
                 /*
                  * Disable the bitmap via an invalid offset. We still cache
                  * the previous bitmap owner and the IO bitmap contents:
@@ -544,6 +560,7 @@ handle_io_bitmap(struct thread_struct *next, struct tss_struct *tss)
                 tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
                 return;
         }
+
         if (likely(next == tss->io_bitmap_owner)) {
                 /*
                  * Previous owner of the bitmap (hence the bitmap content)
@@ -671,20 +688,11 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
                 set_iopl_mask(next->iopl);
 
         /*
-         * Now maybe reload the debug registers
+         * Now maybe handle debug registers and/or IO bitmaps
          */
-        if (unlikely(next->debugreg[7])) {
-                set_debugreg(next->debugreg[0], 0);
-                set_debugreg(next->debugreg[1], 1);
-                set_debugreg(next->debugreg[2], 2);
-                set_debugreg(next->debugreg[3], 3);
-                /* no 4 and 5 */
-                set_debugreg(next->debugreg[6], 6);
-                set_debugreg(next->debugreg[7], 7);
-        }
-
-        if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
-                handle_io_bitmap(next, tss);
+        if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
+            || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
+                __switch_to_xtra(next_p, tss);
 
         disable_tsc(prev_p, next_p);