linux-kernel - Re: TLB flush question (x86

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Message-ID: <CAMzpN2gNtnRVPreeeUVOCr7_t5j6xx+YGHeJkAgqTS2PyUibbw@mail.gmail.com>
Date:	Sat, 17 Sep 2011 19:37:59 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Andreas Mohr <andi@...as.de>
Cc:	Arkaprava Basu <arkaprava.basu@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: TLB flush question (x86_64)

On Sat, Sep 17, 2011 at 3:12 PM, Andreas Mohr <andi@...as.de> wrote:
> Hi,
>
> decided to reply since there hasn't been any activity yet.
>
>> Is there any particular reason why
>> the entire address space is flushed from the tlb while only a range of
>> virtual address space was supposedly required to be flushed?
>
> While this particular function has actually changed in less medieval
> kernel versions, it would be nice if someone knew an answer to that,
> especially since TLB activity may have grave performance implications.
>

x86 hardware can only flush single pages or the whole TLB.  It would
be possible to loop over a small set of pages and invalidate each one,
but the threshold for where that becomes more efficient than flushing
everything is difficult to determine.

--
Brian Gerst
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