linux-kernel - Re: [RFC PATCH 0/3] Fix ebizzy performance regression on IvyBridge due to X86 TLB range flush

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Message-ID: <20131213133517.GA11176@gmail.com>
Date:	Fri, 13 Dec 2013 14:35:17 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Alex Shi <alex.shi@...aro.org>, H Peter Anvin <hpa@...or.com>,
	Linux-X86 <x86@...nel.org>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 0/3] Fix ebizzy performance regression on IvyBridge
 due to X86 TLB range flush


* Mel Gorman <mgorman@...e.de> wrote:

> > [...]
> >
> > stddev appears to be rather large especially around a client count 
> > of 7-8. It will be difficult to fine-tune the TLB range flush 
> > constants if noise is too large.
> 
> The number of iterations were very low to have high confidence of 
> the figures. The high standard deviation for 5 clients was a single 
> large outlier. It potentially could be stabilised to some extent by 
> bumping up the number of iterations a lot and using percentiles 
> instead of means.

Fair enough - and you were bisecting so length of runtime and 
confidence of detection were obviously the primary concerns.

> I'm a bit wary of optimising the TLB flush ranges based on the 
> benchmark even if we stabilised the figures. [...]

Absolutely - but they do appear to be pretty 'adversarial' to the TLB 
optimization, with a measurable slowdown in a pretty complex, 
real-life workload pattern.

So future tuning efforts will have to take such workloads into effect 
as well, to make sure we don't regress again.

Thanks,

	Ingo
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