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

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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>
This commit is contained in:
Stephane Eranian
2006-07-09 21:12:39 -04:00
committed by Linus Torvalds
parent 09075ef0fd
commit b3cf257623
4 changed files with 41 additions and 22 deletions
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50
arch/i386/kernel/process.c
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@@ -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);