[PATCH v4 23/23] powerpc/syscall: Avoid storing 'current' in another pointer
From: Christophe Leroy <hidden>
Date: 2021-01-25 14:59:41
Also in:
lkml
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
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 <redacted> --- arch/powerpc/kernel/syscall.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index 47ae55f94d1c..72e0b18b88d8 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c@@ -186,7 +186,6 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3, struct pt_regs *regs, long scv) { - unsigned long *ti_flagsp = ¤t_thread_info()->flags; unsigned long ti_flags; unsigned long ret = 0;
@@ -202,7 +201,7 @@ 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)))) {
@@ -216,7 +215,7 @@ 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, ¤t_thread_info()->flags); } else { regs->gpr[3] = r3; }
@@ -228,7 +227,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3, again: local_irq_disable(); - 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) {
@@ -244,7 +243,7 @@ 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)) {
--
2.25.0