Messages in this thread Patch in this message | | | From | Christophe Leroy <> | Subject | [PATCH v4 23/23] powerpc/syscall: Avoid storing 'current' in another pointer | Date | Mon, 25 Jan 2021 14:48:36 +0000 (UTC) |
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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> --- 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
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