linux-kernel - Re: [RFC 2/2] x86_64, mm: Reinsert the absent memory

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Message-ID: <20130626144903.GA2210@asylum.americas.sgi.com>
Date:	Wed, 26 Jun 2013 09:49:04 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Nathan Zimmer <nzimmer@....com>, holt@....com, travis@....com,
	rob@...dley.net, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, yinghai@...nel.org, akpm@...ux-foundation.org,
	gregkh@...uxfoundation.org, x86@...nel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC 2/2] x86_64, mm: Reinsert the absent memory

On Wed, Jun 26, 2013 at 02:14:30PM +0200, Ingo Molnar wrote:
> 
> * Nathan Zimmer <nzimmer@....com> wrote:
> 
> > perf seems to struggle with 512 cpus, but I did get some data.
> 
> Btw., mind outlining in what way it struggles?
> 
> Thanks,
> 
> 	Ingo

System interactivity take a nose dive, including the ability to halt perf.
The commands do get through but they take a while.
Other processes tend to make signifigantly reduced progress.
Also it tends to slow down all running processes. 
My guess it is the NMIs overwhelming the system but I have not found a good way
to profile perf gone wild so it is only a guess.

The issue mitigate somewhat by restrictring the number of cpus perf is 
recording or by not using the -g option, but sometimes I do need data on the
whole system.

Nate

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