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