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Date: Fri, 20 Dec 2013 12:18:18 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Alex Shi <alex.shi@linaro.org>, Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Fengguang Wu <fengguang.wu@intel.com>, H Peter Anvin <hpa@zytor.com>,
        Linux-X86 <x86@kernel.org>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB
 range flush v2
Message-ID: <20131220111818.GA23349@gmail.com>
References: <CA+55aFyNAigQqBk07xLpf0nkhZ_x-QkBYG8otRzsqg_8A2eg-Q@mail.gmail.com>
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 <20131216102439.GA21624@gmail.com>
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* Mel Gorman <mgorman@suse.de> wrote:

> On Thu, Dec 19, 2013 at 05:49:25PM +0100, Ingo Molnar wrote:
> > 
> > * Mel Gorman <mgorman@suse.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