RE: [RFC][PATCH v2 00/21] x86/pti: Defer CR3 switch to C code

[David Laight]

From: Alexandre Chartre
> Sent: 18 November 2020 07:42
> 
> 
> On 11/17/20 10:26 PM, Borislav Petkov wrote:
> > On Tue, Nov 17, 2020 at 07:12:07PM +0100, Alexandre Chartre wrote:
> >> Some benchmarks are available, in particular from phoronix:
> >
> > What I was expecting was benchmarks *you* have run which show that
> > perf penalty, not something one can find quickly on the internet and
> > something one cannot always reproduce her-/himself.
> >
> > You do know that presenting convincing numbers with a patchset greatly
> > improves its chances of getting it upstreamed, right?
> >
> 
> Well, it looks like I wrongfully assume that KPTI was a well known performance
> overhead since it was introduced (because it adds extra page-table switches),
> but you are right I should be presenting my own numbers.

IIRC the penalty comes from the page table switch.
Doing it at a different time is unlikely to make much difference.

For some workloads the penalty is massive - getting on for 50%.
We are still using old kernels on AWS.

	David

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