[PATCH v5 09/21] powerpc/64: context tracking remove _TIF_NOHZ

[Christophe Leroy]

Le 13/01/2021 à 08:32, Nicholas Piggin a écrit :
> Add context tracking to the system call handler explicitly, and remove
> _TIF_NOHZ.
> 
> This saves 35 cycles on gettid system call cost on POWER9 with a
> CONFIG_NOHZ_FULL kernel.

35 cycles among 100 cycles, or among 5000 cycles ? I meant what pourcentage to you win ?

Christophe

> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   arch/powerpc/Kconfig                   |  1 -
>   arch/powerpc/include/asm/thread_info.h |  4 +---
>   arch/powerpc/kernel/ptrace/ptrace.c    |  4 ----
>   arch/powerpc/kernel/signal.c           |  4 ----
>   arch/powerpc/kernel/syscall_64.c       | 10 ++++++++++
>   5 files changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 107bb4319e0e..28d5a1b1510f 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -196,7 +196,6 @@ config PPC
>   	select HAVE_STACKPROTECTOR		if PPC64 && $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=r13)
>   	select HAVE_STACKPROTECTOR		if PPC32 && $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=r2)
>   	select HAVE_CONTEXT_TRACKING		if PPC64
> -	select HAVE_TIF_NOHZ			if PPC64
>   	select HAVE_DEBUG_KMEMLEAK
>   	select HAVE_DEBUG_STACKOVERFLOW
>   	select HAVE_DYNAMIC_FTRACE
> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> index 3d8a47af7a25..386d576673a1 100644
> --- a/arch/powerpc/include/asm/thread_info.h
> +++ b/arch/powerpc/include/asm/thread_info.h
> @@ -94,7 +94,6 @@ void arch_setup_new_exec(void);
>   #define TIF_PATCH_PENDING	6	/* pending live patching update */
>   #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
>   #define TIF_SINGLESTEP		8	/* singlestepping active */
> -#define TIF_NOHZ		9	/* in adaptive nohz mode */
>   #define TIF_SECCOMP		10	/* secure computing */
>   #define TIF_RESTOREALL		11	/* Restore all regs (implies NOERROR) */
>   #define TIF_NOERROR		12	/* Force successful syscall return */
> @@ -128,11 +127,10 @@ void arch_setup_new_exec(void);
>   #define _TIF_UPROBE		(1<<TIF_UPROBE)
>   #define _TIF_SYSCALL_TRACEPOINT	(1<<TIF_SYSCALL_TRACEPOINT)
>   #define _TIF_EMULATE_STACK_STORE	(1<<TIF_EMULATE_STACK_STORE)
> -#define _TIF_NOHZ		(1<<TIF_NOHZ)
>   #define _TIF_SYSCALL_EMU	(1<<TIF_SYSCALL_EMU)
>   #define _TIF_SYSCALL_DOTRACE	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
>   				 _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT | \
> -				 _TIF_NOHZ | _TIF_SYSCALL_EMU)
> +				 _TIF_SYSCALL_EMU)
>   
>   #define _TIF_USER_WORK_MASK	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
>   				 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
> diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
> index 3d44b73adb83..4f3d4ff3728c 100644
> --- a/arch/powerpc/kernel/ptrace/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace/ptrace.c
> @@ -262,8 +262,6 @@ long do_syscall_trace_enter(struct pt_regs *regs)
>   {
>   	u32 flags;
>   
> -	user_exit();
> -
>   	flags = READ_ONCE(current_thread_info()->flags) &
>   		(_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
>   
> @@ -340,8 +338,6 @@ void do_syscall_trace_leave(struct pt_regs *regs)
>   	step = test_thread_flag(TIF_SINGLESTEP);
>   	if (step || test_thread_flag(TIF_SYSCALL_TRACE))
>   		tracehook_report_syscall_exit(regs, step);
> -
> -	user_enter();
>   }
>   
>   void __init pt_regs_check(void);
> diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
> index 53782aa60ade..9ded046edb0e 100644
> --- a/arch/powerpc/kernel/signal.c
> +++ b/arch/powerpc/kernel/signal.c
> @@ -282,8 +282,6 @@ static void do_signal(struct task_struct *tsk)
>   
>   void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
>   {
> -	user_exit();
> -
>   	if (thread_info_flags & _TIF_UPROBE)
>   		uprobe_notify_resume(regs);
>   
> @@ -299,8 +297,6 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
>   		tracehook_notify_resume(regs);
>   		rseq_handle_notify_resume(NULL, regs);
>   	}
> -
> -	user_enter();
>   }
>   
>   static unsigned long get_tm_stackpointer(struct task_struct *tsk)
> diff --git a/arch/powerpc/kernel/syscall_64.c b/arch/powerpc/kernel/syscall_64.c
> index dd87b2118620..d7d256a7a41f 100644
> --- a/arch/powerpc/kernel/syscall_64.c
> +++ b/arch/powerpc/kernel/syscall_64.c
> @@ -1,9 +1,11 @@
>   // SPDX-License-Identifier: GPL-2.0-or-later
>   
> +#include <linux/context_tracking.h>
>   #include <linux/err.h>
>   #include <asm/asm-prototypes.h>
>   #include <asm/kup.h>
>   #include <asm/cputime.h>
> +#include <asm/interrupt.h>
>   #include <asm/hw_irq.h>
>   #include <asm/interrupt.h>
>   #include <asm/kprobes.h>
> @@ -28,6 +30,9 @@ notrace long system_call_exception(long r3, long r4, long r5,
>   	if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
>   		BUG_ON(irq_soft_mask_return() != IRQS_ALL_DISABLED);
>   
> +	CT_WARN_ON(ct_state() == CONTEXT_KERNEL);
> +	user_exit_irqoff();
> +
>   	trace_hardirqs_off(); /* finish reconciling */
>   
>   	if (IS_ENABLED(CONFIG_PPC_BOOK3S))
> @@ -182,6 +187,8 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
>   	unsigned long ti_flags;
>   	unsigned long ret = 0;
>   
> +	CT_WARN_ON(ct_state() == CONTEXT_USER);
> +
>   	kuap_check_amr();
>   
>   	regs->result = r3;
> @@ -258,8 +265,11 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
>   		}
>   	}
>   
> +	user_enter_irqoff();
> +
>   	/* scv need not set RI=0 because SRRs are not used */
>   	if (unlikely(!prep_irq_for_enabled_exit(!scv))) {
> +		user_exit_irqoff();
>   		local_irq_enable();
>   		goto again;
>   	}
>