Re: [PATCH qemu-web] Add a blog post on "Micro-Optimizing KVM VM-Exits"

[Kashyap Chamarthy <kchamart@redhat.com>]

[Cc: Rich Jones, addressing his feedback on IRC, below.]

On Fri, Nov 08, 2019 at 10:22:47AM +0100, Kashyap Chamarthy wrote:
> This blog post summarizes the talk "Micro-Optimizing KVM VM-Exits"[1],
> given by Andrea Arcangeli at the recently concluded KVM Forum 2019.
> 
> [1] https://kvmforum2019.sched.com/event/Tmwr/micro-optimizing-kvm-vm-exits-andrea-arcangeli-red-hat-inc
> 
> Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
> ---

[...]

> +The microbechmark: CPUID in a one million loop
> +----------------------------------------------
> +
> +The synthetic microbenchmark (meaning, focus on measuring the
> +performance of a specific area of code) Andrea used was to run the CPUID
> +instruction one million times, without any GCC optimizations or caching.
> +This was done to test the latency of VM-Exits.

I can send a v2 (but will wait for any other feedback), or when applying
someone please replace the above paragraph with the following:

    "Andrea constructed a synthetic microbenchmark program (without any
    GCC optimizations or caching) which runs the CPUID instructions one
    million times in a loop.  This microbenchmark is meant to focus on
    measuring the performance of a specific area of the code -- in this
    case, to test the latency of VM-Exits."

(Rich, hope that reads better.  Thanks for the review.)

> +While stressing that the results of these microbenchmarks do not
> +represent real-world workloads, he had two goals in mind with it: (a)
> +explain how the software mitigation works; and (b) to justify to the
> +broader community the value of the software optimizations he's working
> +on in KVM.
> +
> +Andrea then reasoned through several interesting graphs that show how
> +CPU computation time gets impacted when you disable or enable the
> +various kernel-space mitigations for Spectre v2, L1TF, MDS, et al.

[...]

-- 
/kashyap