linux-kernel - Re: [PATCH 2/2] x86/entry: Inline enter_from_user

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Date:	Fri, 3 Jun 2016 22:08:18 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org.com>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] x86/entry: Inline enter_from_user_mode

On May 30, 2016 5:30 AM, "Paolo Bonzini" <pbonzini@...hat.com> wrote:
>
> This matches what is already done for prepare_exit_to_usermode,
> and saves about 60 clock cycles (4% speedup) with the benchmark
> in the previous commit message.
>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Ingo Molnar <mingo@...nel.org.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/entry/common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index 946bc1a..582bbc8 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -40,7 +40,7 @@ static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs)
>
>  #ifdef CONFIG_CONTEXT_TRACKING
>  /* Called on entry from user mode with IRQs off. */
> -__visible void enter_from_user_mode(void)
> +__visible inline void enter_from_user_mode(void)
>  {
>         CT_WARN_ON(ct_state() != CONTEXT_USER);
>         __user_exit();

I wonder if an extern inline *declaration* is needed as well in this C
file.  At least C99 suggests it is.  Maybe __visible is sufficient to
force an external definition to be emitted.