linux-kernel - Re: [patch] x86: tlb flush avoid superflous leave

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Date:	Tue, 13 Sep 2011 13:35:15 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, hpa@...ux.intel.com
Subject: Re: [patch] x86: tlb flush avoid superflous leave_mm()

On Fri, 2011-09-02 at 15:07 +0800, Shaohua Li wrote:
> If just one page VA tlb is required to be flushed and current task is in lazy
> TLB state, doing leave_mm() is superfluous because it flushes the whole TLB.
> This can reduce some TLB miss.
ping, any comments?

> Signed-off-by: Shaohua Li <shaohua.li@...el.com>
> 
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index d6c0418..3041665 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -153,13 +153,13 @@ void smp_invalidate_interrupt(struct pt_regs *regs)
>  		 */
>  
>  	if (f->flush_mm == percpu_read(cpu_tlbstate.active_mm)) {
> -		if (percpu_read(cpu_tlbstate.state) == TLBSTATE_OK) {
> -			if (f->flush_va == TLB_FLUSH_ALL)
> +		if (f->flush_va == TLB_FLUSH_ALL) {
> +			if (percpu_read(cpu_tlbstate.state) == TLBSTATE_OK)
>  				local_flush_tlb();
>  			else
> -				__flush_tlb_one(f->flush_va);
> +				leave_mm(cpu);
>  		} else
> -			leave_mm(cpu);
> +			__flush_tlb_one(f->flush_va);
>  	}
>  out:
>  	ack_APIC_irq();
> @@ -306,12 +306,8 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long va)
>  
>  	preempt_disable();
>  
> -	if (current->active_mm == mm) {
> -		if (current->mm)
> -			__flush_tlb_one(va);
> -		else
> -			leave_mm(smp_processor_id());
> -	}
> +	if (current->active_mm == mm)
> +		__flush_tlb_one(va);
>  
>  	if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
>  		flush_tlb_others(mm_cpumask(mm), mm, va);
> 


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