Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

Hi Andrew,

On 26/09/2017 01:34, Andrew Morton wrote:
> On Mon, 25 Sep 2017 09:27:43 -0700 Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:
>
> > On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
> > <ldufour@xxxxxxxxxxxxxxxxxx> wrote:
> > > Despite the unprovable lockdep warning raised by Sergey, I didn't get any
> > > feedback on this series.
> > >
> > > Is there a chance to get it moved upstream ?
> >
> > what is the status ?
> > We're eagerly looking forward for this set to land,
> > since we have several use cases for tracing that
> > will build on top of this set as discussed at Plumbers.
>
> There has been sadly little review and testing so far :(
>
> I'll be taking a close look at it all over the next couple of weeks.
>
> One terribly important thing (especially for a patchset this large and
> intrusive) is the rationale for merging it: the justification, usually
> in the form of end-user benefit.
>
> 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.

Thanks,
Laurent

> If you have additional usecases then please, spell them out for us in
> full detail so we can better understand the benefits which this
> patchset provides.