linux-kernel - Re: [PATCH -v3 14/14] x86, mm: Map ISA area with connected ram range at the same time

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Message-ID: <CAOJsxLGXQ9+5uEvq-Pfxt=zZLWR3ZmR1WPeN=pzdzQVjHWrd0g@mail.gmail.com>
Date:	Wed, 5 Sep 2012 11:02:33 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, Jacob Shin <jacob.shin@....com>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v3 14/14] x86, mm: Map ISA area with connected ram range
 at the same time

On Wed, Sep 5, 2012 at 8:46 AM, Yinghai Lu <yinghai@...nel.org> wrote:
> so could reduce one loop.
>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>

How significant is the speed gain? The "isa_done" flag makes code flow
more difficult to follow.

> ---
>  arch/x86/mm/init.c |   21 ++++++++++++++-------
>  1 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 6663f61..e69f832 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -248,20 +248,27 @@ static void __init walk_ram_ranges(
>                         void *data)
>  {
>         unsigned long start_pfn, end_pfn;
> +       bool isa_done = false;
>         int i;
>
> -       /* the ISA range is always mapped regardless of memory holes */
> -       work_fn(0, ISA_END_ADDRESS, data);
> -
>         for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, NULL) {
>                 u64 start = start_pfn << PAGE_SHIFT;
>                 u64 end = end_pfn << PAGE_SHIFT;
>
> -               if (end <= ISA_END_ADDRESS)
> -                       continue;
> +               if (!isa_done && start > ISA_END_ADDRESS) {
> +                       work_fn(0, ISA_END_ADDRESS, data);
> +                       isa_done = true;
> +               } else {
> +                       if (end < ISA_END_ADDRESS)
> +                               continue;
> +
> +                       if (start <= ISA_END_ADDRESS &&
> +                           end >= ISA_END_ADDRESS) {
> +                               start = 0;
> +                               isa_done = true;
> +                       }
> +               }
>
> -               if (start < ISA_END_ADDRESS)
> -                       start = ISA_END_ADDRESS;
>  #ifdef CONFIG_X86_32
>                 /* on 32 bit, we only map up to max_low_pfn */
>                 if ((start >> PAGE_SHIFT) >= max_low_pfn)
> --
> 1.7.7
>
> --
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