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

Thomas Gleixner
2018-03-27T17:51:16Z

On Tue, 27 Mar 2018, Dave Hansen wrote:

> On 03/27/2018 06:36 AM, Thomas Gleixner wrote:
> >> User Time Kernel Time Clock Elapsed
> >> Baseline ( 0 GLB PTEs) 803.79 67.77 237.30
> >> w/series (28 GLB PTEs) 807.70 (+0.7%) 68.07 (+0.7%) 238.07 (+0.3%)
> >>
> >> Without PCIDs, it behaves the way I would expect.
> > What's the performance benefit on !PCID systems? And I mean systems which
> > actually do not have PCID, not a PCID system with 'nopcid' on the command
> > line.
>
> Do you have something in mind for this? Basically *all* of the servers
> that I have access to have PCID because they are newer than ~7 years old.
>
> That leaves *some* Ivybridge and earlier desktops, Atoms and AMD

AMD is not interesting as it's not PTI and uses GLOBAL anyway.

> 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.

Thanks,

tglx