[PATCH v5 20/22] powerpc/syscall: Avoid storing 'current' in another pointer

Christophe Leroy
2021-02-08T16:38:54Z

By saving the pointer pointing to thread_info.flags, gcc copies r2
in a non-volatile register.

We know 'current' doesn't change, so avoid that intermediaite pointer.

Reduces null_syscall benchmark by 2 cycles (322 => 320 cycles)

On PPC64, gcc seems to know that 'current' is not changing, and it keeps
it in a non volatile register to avoid multiple read of 'current' in paca.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
v5: Also in interrupt exit prepare
---
arch/powerpc/kernel/interrupt.c | 28 +++++++++++-----------------
1 file changed, 11 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 8c38e8c95be2..c89a8eac3e24 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -223,7 +223,6 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
struct pt_regs *regs,
long scv)
{
- unsigned long *ti_flagsp = &current_thread_info()->flags;
unsigned long ti_flags;
unsigned long ret = 0;

@@ -241,7 +240,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
/* Check whether the syscall is issued inside a restartable sequence */
rseq_syscall(regs);

- ti_flags = *ti_flagsp;
+ ti_flags = current_thread_info()->flags;

if (unlikely(r3 >= (unsigned long)-MAX_ERRNO) && !scv) {
if (likely(!(ti_flags & (_TIF_NOERROR | _TIF_RESTOREALL)))) {
@@ -255,7 +254,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
ret = _TIF_RESTOREALL;
else
regs->gpr[3] = r3;
- clear_bits(_TIF_PERSYSCALL_MASK, ti_flagsp);
+ clear_bits(_TIF_PERSYSCALL_MASK, &current_thread_info()->flags);
} else {
regs->gpr[3] = r3;
}
@@ -268,7 +267,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
local_irq_disable();

again:
- ti_flags = READ_ONCE(*ti_flagsp);
+ ti_flags = READ_ONCE(current_thread_info()->flags);
while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
local_irq_enable();
if (ti_flags & _TIF_NEED_RESCHED) {
@@ -284,7 +283,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
do_notify_resume(regs, ti_flags);
}
local_irq_disable();
- ti_flags = READ_ONCE(*ti_flagsp);
+ ti_flags = READ_ONCE(current_thread_info()->flags);
}

if (IS_ENABLED(CONFIG_PPC_BOOK3S) && IS_ENABLED(CONFIG_PPC_FPU)) {
@@ -339,10 +338,6 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
#ifndef CONFIG_PPC_BOOK3E_64 /* BOOK3E not yet using this */
notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned long msr)
{
-#ifdef CONFIG_PPC_BOOK3E
- struct thread_struct *ts = &current->thread;
-#endif
- unsigned long *ti_flagsp = &current_thread_info()->flags;
unsigned long ti_flags;
unsigned long flags;
unsigned long ret = 0;
@@ -365,7 +360,7 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned
local_irq_save(flags);

again:
- ti_flags = READ_ONCE(*ti_flagsp);
+ ti_flags = READ_ONCE(current_thread_info()->flags);
while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
local_irq_enable(); /* returning to user: may enable */
if (ti_flags & _TIF_NEED_RESCHED) {
@@ -376,7 +371,7 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned
do_notify_resume(regs, ti_flags);
}
local_irq_disable();
- ti_flags = READ_ONCE(*ti_flagsp);
+ ti_flags = READ_ONCE(current_thread_info()->flags);
}

if (IS_ENABLED(CONFIG_PPC_BOOK3S) && IS_ENABLED(CONFIG_PPC_FPU)) {
@@ -407,13 +402,13 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned
}

#ifdef CONFIG_PPC_BOOK3E
- if (unlikely(ts->debug.dbcr0 & DBCR0_IDM)) {
+ if (unlikely(current->thread.debug.dbcr0 & DBCR0_IDM)) {
/*
* Check to see if the dbcr0 register is set up to debug.
* Use the internal debug mode bit to do this.
*/
mtmsr(mfmsr() & ~MSR_DE);
- mtspr(SPRN_DBCR0, ts->debug.dbcr0);
+ mtspr(SPRN_DBCR0, current->thread.debug.dbcr0);
mtspr(SPRN_DBSR, -1);
}
#endif
@@ -438,7 +433,6 @@ void preempt_schedule_irq(void);

notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsigned long msr)
{
- unsigned long *ti_flagsp = &current_thread_info()->flags;
unsigned long flags;
unsigned long ret = 0;
#ifdef CONFIG_PPC64
@@ -461,8 +455,8 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsign
amr = kuap_get_and_check_amr();
#endif

- if (unlikely(*ti_flagsp & _TIF_EMULATE_STACK_STORE)) {
- clear_bits(_TIF_EMULATE_STACK_STORE, ti_flagsp);
+ if (unlikely(current_thread_info()->flags & _TIF_EMULATE_STACK_STORE)) {
+ clear_bits(_TIF_EMULATE_STACK_STORE, &current_thread_info()->flags);
ret = 1;
}

@@ -474,7 +468,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsign
again:
if (IS_ENABLED(CONFIG_PREEMPT)) {
/* Return to preemptible kernel context */
- if (unlikely(*ti_flagsp & _TIF_NEED_RESCHED)) {
+ if (unlikely(current_thread_info()->flags & _TIF_NEED_RESCHED)) {
if (preempt_count() == 0)
preempt_schedule_irq();
}
--
2.25.0