linux-kernel - Re: [PATCH 3/3] x86: mm: Account for the of CPUs that must be flushed during a TLB range flush

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Date:	Thu, 12 Dec 2013 21:41:55 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	Mel Gorman <mgorman@...e.de>
CC:	H Peter Anvin <hpa@...or.com>, Linux-X86 <x86@...nel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] x86: mm: Account for the of CPUs that must be flushed
 during a TLB range flush

On 12/12/2013 07:55 PM, Mel Gorman wrote:
> X86 TLB range flushing uses a balance point to decide if a single global TLB
> flush or multiple single page flushes would perform best.  This patch takes into
> account how many CPUs must be flushed.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>  arch/x86/mm/tlb.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 09b8cb8..0cababa 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -217,6 +217,9 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
>  	act_entries = mm->total_vm > act_entries ? act_entries : mm->total_vm;
>  	nr_base_pages = (end - start) >> PAGE_SHIFT;
>  
> +	/* Take the number of CPUs to range flush into account */
> +	nr_base_pages *= cpumask_weight(mm_cpumask(mm));
> +

flush range calculation base on per cpu, since no matter how many cpus
in the process, tlb flush and refill time won't change.
>  	/* tlb_flushall_shift is on balance point, details in commit log */
>  	if (nr_base_pages > act_entries || has_large_page(mm, start, end)) {
>  		count_vm_event(NR_TLB_LOCAL_FLUSH_ALL);
> 


-- 
Thanks
    Alex
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