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x86/process: Optimize TIF checks in __switch_to_xtra()

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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.

With default defconfigs for each arch,

x86_64: arch/x86/kernel/process.o
text       data     bss     dec     hex
3056       8577      16   11649    2d81	Before
3024	   8577      16	  11617	   2d61	After

i386: arch/x86/kernel/process.o
text       data     bss     dec     hex
2957	   8673	      8	  11638	   2d76	Before
2925	   8673       8	  11606	   2d56	After

Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Link: http://lkml.kernel.org/r/20170214081104.9244-2-khuey@kylehuey.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Kyle Huey 2017-02-14 00:11:02 -08:00 committed by Thomas Gleixner
parent 434fd6353b
commit af8b3cd393
1 changed files with 37 additions and 30 deletions
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67
arch/x86/kernel/process.c
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@ -182,54 +182,61 @@ int set_tsc_mode(unsigned int val)
return 0;
}
void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
struct tss_struct *tss)
static inline void switch_to_bitmap(struct tss_struct *tss,
struct thread_struct *prev,
struct thread_struct *next,
unsigned long tifp, unsigned long tifn)
{
struct thread_struct *prev, *next;
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)) {
unsigned long debugctl = get_debugctlmsr();
debugctl &= ~DEBUGCTLMSR_BTF;
if (test_tsk_thread_flag(next_p, 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))
hard_disable_TSC();
else
hard_enable_TSC();
}
if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
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));
/*
* Make sure that the TSS limit is correct for the CPU
* to notice the IO bitmap.
*/
refresh_tss_limit();
} else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
} 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;
tifn = READ_ONCE(task_thread_info(next_p)->flags);
tifp = READ_ONCE(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 (tifn & _TIF_BLOCKSTEP)
debugctl |= DEBUGCTLMSR_BTF;
update_debugctlmsr(debugctl);
}
if ((tifp ^ tifn) & _TIF_NOTSC) {
if (tifn & _TIF_NOTSC)
hard_disable_TSC();
else
hard_enable_TSC();
}
}
/*