From: Stephane Eranian <[email protected]>
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 <[email protected]>
Signed-off-by: Chuck Ebbert <[email protected]>
Acked-by: Andi Kleen <[email protected]>
---
arch/i386/kernel/ioport.c | 1
arch/i386/kernel/process.c | 50 +++++++++++++++++++++++------------------
arch/i386/kernel/ptrace.c | 5 +++-
include/asm-i386/thread_info.h | 7 +++++
4 files changed, 41 insertions(+), 22 deletions(-)
--- 2.6.18-rc1-nb.orig/arch/i386/kernel/ioport.c
+++ 2.6.18-rc1-nb/arch/i386/kernel/ioport.c
@@ -79,6 +79,7 @@ asmlinkage long sys_ioperm(unsigned long
memset(bitmap, 0xff, IO_BITMAP_BYTES);
t->io_bitmap_ptr = bitmap;
+ set_thread_flag(TIF_IO_BITMAP);
}
/*
--- 2.6.18-rc1-nb.orig/arch/i386/kernel/process.c
+++ 2.6.18-rc1-nb/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 cl
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 cl
}
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 *t
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 *n
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_t
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);
--- 2.6.18-rc1-nb.orig/arch/i386/kernel/ptrace.c
+++ 2.6.18-rc1-nb/arch/i386/kernel/ptrace.c
@@ -468,8 +468,11 @@ long arch_ptrace(struct task_struct *chi
for(i=0; i<4; i++)
if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
goto out_tsk;
+ if (data)
+ set_tsk_thread_flag(child, TIF_DEBUG);
+ else
+ clear_tsk_thread_flag(child, TIF_DEBUG);
}
-
addr -= (long) &dummy->u_debugreg;
addr = addr >> 2;
child->thread.debugreg[addr] = data;
--- 2.6.18-rc1-nb.orig/include/asm-i386/thread_info.h
+++ 2.6.18-rc1-nb/include/asm-i386/thread_info.h
@@ -140,6 +140,8 @@ static inline struct thread_info *curren
#define TIF_SECCOMP 8 /* secure computing */
#define TIF_RESTORE_SIGMASK 9 /* restore signal mask in do_signal() */
#define TIF_MEMDIE 16
+#define TIF_DEBUG 17 /* uses debug registers */
+#define TIF_IO_BITMAP 18 /* uses I/O bitmap */
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
@@ -151,6 +153,8 @@ static inline struct thread_info *curren
#define _TIF_SYSCALL_AUDIT (1<<TIF_SYSCALL_AUDIT)
#define _TIF_SECCOMP (1<<TIF_SECCOMP)
#define _TIF_RESTORE_SIGMASK (1<<TIF_RESTORE_SIGMASK)
+#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 \
@@ -159,6 +163,9 @@ static inline struct thread_info *curren
/* work to do on any return to u-space */
#define _TIF_ALLWORK_MASK (0x0000FFFF & ~_TIF_SECCOMP)
+/* flags to check in __switch_to() */
+#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)
+
/*
* Thread-synchronous status.
*
--
Chuck
"You can't read a newspaper if you can't read." --George W. Bush
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