Help the compiler to avoid reevaluating the thread flags for each checked
bit by reordering the bit checks and providing an explicit xor for
evaluation.
x8664: arch/x86/kernel/process.o
text data bss dec hex
3726 8505 16 12247 2fd7 Before
3694 8505 16 12215 2fb7 After
i386: No change
Originally-from: Kyle Huey <kh...@kylehuey.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
arch/x86/kernel/process.c | 54 ++++++++++++++++++++++++++--------------------
1 file changed, 31 insertions(+), 23 deletions(-)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -174,48 +174,56 @@ int set_tsc_mode(unsigned int val)
return 0;
}
+static inline void switch_to_bitmap(struct tss_struct *tss,
+ struct thread_struct *prev,
+ struct thread_struct *next,
+ unsigned long tifp, unsigned long tifn)
+{
+ if (tifn & _TIF_IO_BITMAP) {
+ /*
+ * Copy the relevant range of the IO bitmap.
+ * Normally this is 128 bytes or less:
+ */
+ memcpy(tss->io_bitmap, next->io_bitmap_ptr,
+ max(prev->io_bitmap_max, next->io_bitmap_max));
+ } else if (tifp & _TIF_IO_BITMAP) {
+ /*
+ * Clear any possible leftover bits:
+ */
+ memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
+ }
+}
+
void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
struct tss_struct *tss)
{
struct thread_struct *prev, *next;
+ unsigned long tifp, tifn;
prev = &prev_p->thread;
next = &next_p->thread;
- if (test_tsk_thread_flag(prev_p, TIF_BLOCKSTEP) ^
- test_tsk_thread_flag(next_p, TIF_BLOCKSTEP)) {
+ tifn = task_thread_info(next_p)->flags;
+ tifp = task_thread_info(prev_p)->flags;
+ switch_to_bitmap(tss, prev, next, tifp, tifn);
+
+ propagate_user_return_notify(prev_p, next_p);
+
+ if ((tifp ^ tifn) & _TIF_BLOCKSTEP) {
unsigned long debugctl = get_debugctlmsr();
debugctl &= ~DEBUGCTLMSR_BTF;
- if (test_tsk_thread_flag(next_p, TIF_BLOCKSTEP))
+ if (tifn & _TIF_BLOCKSTEP)
debugctl |= DEBUGCTLMSR_BTF;
-
update_debugctlmsr(debugctl);
}
- if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
- test_tsk_thread_flag(next_p, TIF_NOTSC)) {
- /* prev and next are different */
- if (test_tsk_thread_flag(next_p, TIF_NOTSC))
+ if ((tifp ^ tifn) & _TIF_NOTSC) {
+ if (tifn & _TIF_NOTSC)
hard_disable_TSC();
else
hard_enable_TSC();
}
-
- if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
- /*
- * Copy the relevant range of the IO bitmap.
- * Normally this is 128 bytes or less:
- */
- memcpy(tss->io_bitmap, next->io_bitmap_ptr,
- max(prev->io_bitmap_max, next->io_bitmap_max));
- } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
- /*
- * Clear any possible leftover bits:
- */
- memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
- }
- propagate_user_return_notify(prev_p, next_p);
}
/*
