linux-kernel - Re: [v7 0/8] Reduce cross CPU IPI interference

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Date:	Fri, 10 Feb 2012 19:39:08 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
Cc:	Chris Metcalf <cmetcalf@...era.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	linux-mm@...ck.org, Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Avi Kivity <avi@...hat.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Kosaki Motohiro <kosaki.motohiro@...il.com>,
	Milton Miller <miltonm@....com>
Subject: Re: [v7 0/8] Reduce cross CPU IPI interference

On Sun, 2012-02-05 at 13:46 +0200, Gilad Ben-Yossef wrote:
> > /*
> >  * Cause all memory mappings to be populated in the page table.
> >  * Specifying this when entering dataplane mode ensures that no future
> >  * page fault events will occur to cause interrupts into the Linux
> >  * kernel, as long as no new mappings are installed by mmap(), etc.
> >  * Note that since the hardware TLB is of finite size, there will
> >  * still be the potential for TLB misses that the hypervisor handles,
> >  * either via its software TLB cache (fast path) or by walking the
> >  * kernel page tables (slow path), so touching large amounts of memory
> >  * will still incur hypervisor interrupt overhead.
> >  */
> > #define DP_POPULATE     0x8
> 
> hmm... I've probably missed something, but doesn't this replicate
> mlockall (MCL_CURRENT|MCL_FUTURE) ? 

Never use mlockall() its a sign you're doing it wrong, also his comment
seems to imply MCL_FUTURE isn't required.

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