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

Ingo Molnar
2018-03-30T12:17:31Z

* Ingo Molnar <mingo@kernel.org> wrote:

> > 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.

BTW., the expectation on !PCID Intel hardware would be for global pages to help
even more than the 0.6% and 1.7% you measured on PCID hardware: PCID already
_reduces_ the cost of TLB flushes - so if there's not even PCID then global pages
should help even more.

In theory at least. Would still be nice to measure it.

Thanks,

Ingo