linux-kernel - Re: [PATCH 3/3] x86: add local_tlb_flush_kernel

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Date:	Mon, 25 Jun 2012 19:01:26 -0400
From:	Konrad Rzeszutek Wilk <konrad@...nok.org>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] x86: add local_tlb_flush_kernel_range()

On Mon, Jun 25, 2012 at 12:14 PM, Seth Jennings
<sjenning@...ux.vnet.ibm.com> wrote:
> This patch adds support for a local_tlb_flush_kernel_range()
> function for the x86 arch.  This function allows for CPU-local
> TLB flushing, potentially using invlpg for single entry flushing,
> using an arch independent function name.

What x86 hardware did you use to figure the optimal number?

>
> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> ---
>  arch/x86/include/asm/tlbflush.h |   21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index 36a1a2a..92a280b 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -168,4 +168,25 @@ static inline void flush_tlb_kernel_range(unsigned long start,
>        flush_tlb_all();
>  }
>
> +#define __HAVE_LOCAL_FLUSH_TLB_KERNEL_RANGE
> +/*
> + * INVLPG_BREAK_EVEN_PAGES is the number of pages after which single tlb
> + * flushing becomes more costly than just doing a complete tlb flush.
> + * While this break even point varies among x86 hardware, tests have shown
> + * that 8 is a good generic value.
> +*/
> +#define INVLPG_BREAK_EVEN_PAGES 8
> +static inline void local_flush_tlb_kernel_range(unsigned long start,
> +               unsigned long end)
> +{
> +       if (cpu_has_invlpg &&
> +               (end - start)/PAGE_SIZE <= INVLPG_BREAK_EVEN_PAGES) {
> +               while (start < end) {
> +                       __flush_tlb_single(start);
> +                       start += PAGE_SIZE;
> +               }
> +       } else
> +               local_flush_tlb();
> +}
> +
>  #endif /* _ASM_X86_TLBFLUSH_H */
> --
> 1.7.9.5
>
> --
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