[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 94e2c87edea..923bb292f47 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);