linux-kernel - Re: [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB range flush v2

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Message-ID: <20131220111818.GA23349@gmail.com>
Date:	Fri, 20 Dec 2013 12:18:18 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alex Shi <alex.shi@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	H Peter Anvin <hpa@...or.com>, Linux-X86 <x86@...nel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB
 range flush v2


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

> On Thu, Dec 19, 2013 at 05:49:25PM +0100, Ingo Molnar wrote:
> > 
> > * Mel Gorman <mgorman@...e.de> wrote:
> > 
> > > [...]
> > > 
> > > Because we lack data on TLB range flush distributions I think we 
> > > should still go with the conservative choice for the TLB flush 
> > > shift. The worst case is really bad here and it's painfully obvious 
> > > on ebizzy.
> > 
> > So I'm obviously much in favor of this - I'd in fact suggest 
> > making the conservative choice on _all_ CPU models that have 
> > aggressive TLB range values right now, because frankly the testing 
> > used to pick those values does not look all that convincing to me.
> 
> I think the choices there are already reasonably conservative. I'd 
> be reluctant to support merging a patch that made a choice on all 
> CPU models without having access to the machines to run tests on. I 
> don't see the Intel people volunteering to do the necessary testing.

So based on this thread I lost confidence in test results on all CPU 
models but the one you tested.

I see two workable options right now:

 - We turn the feature off on all other CPU models, until someone
   measures and tunes them reliably.

or

 - We make all tunings that are more aggressive than yours to match
   yours. In the future people can measure and argue for more
   aggressive tunings.

Thanks,

	Ingo
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