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

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Message-ID: <4FEA9FDD.6030102@kernel.org>
Date:	Wed, 27 Jun 2012 14:53:33 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>, Alex Shi <alex.shi@...el.com>
Subject: Re: [PATCH 3/3] x86: add local_tlb_flush_kernel_range()

On 06/26/2012 01:14 AM, Seth Jennings 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.
> 
> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>


Anyway, we don't matter INVLPG_BREAK_EVEN_PAGES's optimization point is 8 or something.
We do care only it works without big problem.
I believe after Alex's patch is settle down, we can fix it if it's wrong.
But it shouldn't prevent merging this patch.

Acked-by: Minchan Kim <minchan@...nel.org>

Nitpick: I expect you change __HAVE_LOCAL_XXX to __HAVE_ARCH_LOCAL_XXX in next spin. :)


> ---
>  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 */



-- 
Kind regards,
Minchan Kim
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