In-Reply-To: <[email protected]>
On Tue, 4 Jul 2006 00:29:39 -0700, Stephane Eranian wrote:
> 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.
I get a 5-10% speedup in task switch times with this patch.
Some very minor comments:
> <signed-off-by>: [email protected]
Should be: Signed-off-by: Stephane Eranian <[email protected]>
> + if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP) == 0) {
preferred:
if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> @@ -674,18 +692,9 @@ struct task_struct fastcall * __switch_t
> /*
> * Now maybe reload the debug registers
> */
/*
* Now maybe reload the debug registers and/or IO bitmap
*/
And this should be added to the patch:
--- 2.6.17-nb.orig/arch/i386/kernel/process.c
+++ 2.6.17-nb/arch/i386/kernel/process.c
@@ -360,13 +360,12 @@ 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))) {
int cpu = get_cpu();
struct tss_struct *tss = &per_cpu(init_tss, cpu);
+ struct task_struct *tsk = current;
+ struct thread_struct *t = &tsk->thread;
kfree(t->io_bitmap_ptr);
t->io_bitmap_ptr = NULL;
--
Chuck
"You can't read a newspaper if you can't read." --George W. Bush
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