Re: [PATCH 00/11] Use global pages with PTI

[Ingo Molnar]

* Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote:

> On 03/27/2018 01:07 PM, Ingo Molnar wrote:
> > * Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> >>> systems.  Atoms are going to be the easiest thing to get my hands on,
> >>> but I tend to shy away from them for performance work.
> >> What I have in mind is that I wonder whether the whole circus is worth it
> >> when there is no performance advantage on PCID systems.
> 
> I was waiting on trying to find a relatively recent Atom system (they
> actually come in reasonably sized servers [1]), but I'm hitting a snag
> there, so I figured I'd just share a kernel compile using Ingo's
> perf-based methodology on a Skylake desktop system with PCIDs.
>
> Here's the kernel compile:
> 
> No Global pages (baseline): 186.951 seconds time elapsed  ( +-  0.35% )
> 28 Global pages (this set): 185.756 seconds time elapsed  ( +-  0.09% )
>                              -1.195 seconds (-0.64%)
> 
> Lower is better here, obviously.
> 
> I also re-checked everything using will-it-scale's llseek1 test[2] which
> is basically a microbenchmark of a halfway reasonable syscall.  Higher
> here is better.
> 
> No Global pages (baseline): 15783951 lseeks/sec
> 28 Global pages (this set): 16054688 lseeks/sec
> 			     +270737 lseeks/sec (+1.71%)
> 
> So, both the kernel compile and the microbenchmark got measurably faster.

Ok, cool, this is much better!

Mind re-sending the patch-set against latest -tip so it can be merged?

At this point !PCID Intel hardware is not a primary concern, if something bad 
happens on them with global pages we can quirk global pages off on them in some 
way, or so.

Thanks,

	Ingo