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

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Date:	Tue, 26 Apr 2011 09:22:52 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Geunsik Lim <leemgs1@...il.com>
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, 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?

-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.

Then again, what's the point, simply remove the whole thing (like I did)
and your problem is solved too.


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