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

[Laurent Dufour]

Hi,

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 do agree and I could just encourage people to do so :/

> I'll be taking a close look at it all over the next couple of weeks.

Thanks Andrew for giving it a close look.

> 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.

The benefit is only for multi-threaded processes. But even on *small* 
systems with 16 CPUs, there is a real 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(?).

I did test with kernbench, involving gcc/ld which are not 
multi-threaded, AFAIK, and I didn't see any impact.
But if you know additional test I should give a try, please advise.

Regarding ebizzy, it was designed to simulate web server's activity, so 
I guess there will be improvements when running real web servers.

>  Even things as simple as impact upon
> single-threaded pagefault-intensive workloads and its effect upon
> CONFIG_SMP=n .text size?
>
> 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.

The other use-case I'm aware of is on memory database, where performance 
improvements is really significant, as I mentioned in the header of my 
series.

Cheers,
Laurent.