powerpc/syscall: Avoid storing 'current' in another pointer

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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ad0363ff0ff8c125f40e1cdc589a85bbd7e31693.1612946484.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index f93664ad4a5e25699bee63a0e656d8a826e2ac4a..398cd86b6ada15514774666dbcfcebc7bd178a33 100644 (file)
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -241,7 +241,6 @@ 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;
        bool is_not_scv = !IS_ENABLED(CONFIG_PPC_BOOK3S_64) || !scv;
@@ -257,7 +256,7 @@ 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) && is_not_scv) {
                if (likely(!(ti_flags & (_TIF_NOERROR | _TIF_RESTOREALL)))) {
@@ -271,7 +270,7 @@ 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;
        }
@@ -284,7 +283,7 @@ 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) {
@@ -300,7 +299,7 @@ again:
                        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)) {
@@ -357,7 +356,6 @@ again:
 #ifndef CONFIG_PPC_BOOK3E_64 /* BOOK3E not yet using this */
 notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned long msr)
 {
-       unsigned long *ti_flagsp = &current_thread_info()->flags;
        unsigned long ti_flags;
        unsigned long flags;
        unsigned long ret = 0;
@@ -380,7 +378,7 @@ 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) {
@@ -391,7 +389,7 @@ again:
                        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)) {
@@ -443,7 +441,6 @@ 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
@@ -466,8 +463,8 @@ 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;
        }
 
@@ -479,7 +476,7 @@ 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();
                        }