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

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Message-ID: <4FEB5267.8000109@linux.vnet.ibm.com>
Date:	Wed, 27 Jun 2012 13:35:19 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Minchan Kim <minchan@...nel.org>,
	Alex Shi <alex.shi@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org, 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>
Subject: Re: [PATCH 3/3] x86: add local_tlb_flush_kernel_range()

On 06/27/2012 10:39 AM, Konrad Rzeszutek Wilk wrote:
> On Wed, Jun 27, 2012 at 08:12:56AM -0700, Dan Magenheimer wrote:
>>> From: Minchan Kim [mailto:minchan@...nel.org]
>>> Subject: Re: [PATCH 3/3] x86: add local_tlb_flush_kernel_range()
>>>
>>> Hello,
>>>
>>> On 06/27/2012 03:14 PM, Alex Shi wrote:
>>>
>>>> On 06/27/2012 01:53 PM, Minchan Kim wrote:
>>>>
>>>>> 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.
>>>>
>>>>
>>>> Different CPU type has different balance point on the invlpg replacing
>>>> flush all. and some CPU never get benefit from invlpg, So, it's better
>>>> to use different value for different CPU, not a fixed
>>>> INVLPG_BREAK_EVEN_PAGES.
>>>
>>> I think it could be another patch as further step and someone who are
>>> very familiar with architecture could do better than.
>>> So I hope it could be merged if it doesn't have real big problem.
>>>
>>> Thanks for the comment, Alex.
>>
>> Just my opinion, but I have to agree with Alex.  Hardcoding
>> behavior that is VERY processor-specific is a bad idea.  TLBs should
>> only be messed with when absolutely necessary, not for the
>> convenience of defending an abstraction that is nice-to-have
>> but, in current OS kernel code, unnecessary.
> 
> At least put a big fat comment in the patch saying:
> "This is based on research done by Alex, where ...

I can do this.

--
Seth

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