Messages in this thread | | | From | David Laight <> | Subject | RE: [RFC][PATCH v2 00/21] x86/pti: Defer CR3 switch to C code | Date | Wed, 18 Nov 2020 09:30:01 +0000 |
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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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