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Date: Thu, 28 Sep 2017 13:38:50 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
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Subject: Re: [PATCH v3 00/20] Speculative page faults
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On Thu, 28 Sep 2017 14:29:02 +0200 Laurent Dufour <ldufour@linux.vnet.ibm.com> wrote:

> > Laurent's [0/n] provides some nice-looking performance benefits for
> > workloads which are chosen to show performance benefits(!) but, alas,
> > no quantitative testing results for workloads which we may suspect will
> > be harmed by the changes(?).  Even things as simple as impact upon
> > single-threaded pagefault-intensive workloads and its effect upon
> > CONFIG_SMP=n .text size?
> 
> I forgot to mention in my previous email the impact on the .text section.
> 
> Here are the metrics I got :
> 
> .text size	UP		SMP		Delta
> 4.13-mmotm	8444201		8964137		6.16%
> '' +spf		8452041		8971929		6.15%
> 	Delta	0.09%		0.09%	
> 
> No major impact as you could see.

8k text increase seems rather a lot actually.  That's a lot more
userspace cacheclines that get evicted during a fault...

Is the feature actually beneficial on uniprocessor?