linux-kernel - Re: [PATCH 0/4] munmap: Flexible mem unmap operation interface for scheduling latency

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Date:	Wed, 27 Apr 2011 08:57:24 +0900
From:	Geunsik Lim <leemgs1@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH 0/4] munmap: Flexible mem unmap operation interface for
 scheduling latency

On Tue, Apr 26, 2011 at 4:22 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Tue, 2011-04-26 at 10:20 +0900, Geunsik Lim wrote:
>> Yes. I also checked the patch that you stated at LKML mailing list previously.
>> In my thinking. I want to keep ZAP_BLOCK_SIZE related contents
>> that adjusted by Ingo, Robert, Andrew, and so on a long time ago
>> because I believe that we can overcome below problems sufficiently
>> in real world.
>> . LKML archive - http://lkml.org/lkml/2002/7/24/273
>> . LKML archive - http://lkml.org/lkml/2004/9/14/101
>
> Real ancient world, that was 2004, well before we grew preemptible
> mmu_gather.
>
>> In my experience, I did overcome below problems with this patch
>> based on ZAP_BLOCK_SIZE.
>>
>> 1) To solve temporal CPU contention
>>     (e.g: case that cpu contention is 93% ~ 96% according to mmap/munmap
>>             to access mass files )
>> 2) To get real-time or real-fast selectively on specified linux system
>
> I still don't get it, what kernel are you targeting here and why?
In my case, I tested at embedded target(e.g: 2.6.29 , 2.6.32) based on
arm cortex-a series for user responsiveness when trying to access mass files.
>
> -RT doesn't care, and clearly PREEMPT=n doesn't care because its not
> about latency at all, the only half-way point is PREEMPT=y and for that
> you could simply reduce ZAP_BLOCK_SIZE.
Thank you for your reviews.  yes. we can simply reduce ZAP_BLOCK_SIZE.
I mean that we can control ZAP_BLOCK_SIZE after consider a suitable
munmap() operation size both preemptive mode and non-preemptive mode.
>
> Then again, what's the point, simply remove the whole thing (like I did)
> and your problem is solved too.
If we can get real-fast or real-time with advanced preemptive mmu_gather
sufficiently according to user needs sometimes, I also think that
that's good certainly.
>
>
>



-- 
Regards,
Geunsik Lim ( Samsung Electronics )
Blog : http://blog.naver.com/invain/
e-Mail: geunsik.lim@...sung.com
           leemgs@...il.com , leemgs1@...il.com
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