kvm/arm64: Spark benchmark

[Yu Zhao]

On Fri, Jun 9, 2023 at 7:04 AM Marc Zyngier <maz at kernel.org> wrote:
>
> On Fri, 09 Jun 2023 01:59:35 +0100,
> Yu Zhao <yuzhao at google.com> wrote:
> >
> > TLDR
> > ====
> > Apache Spark spent 12% less time sorting four billion random integers twenty times (in ~4 hours) after this patchset [1].
>
> Why are the 3 architectures you have considered being evaluated with 3
> different benchmarks?

I was hoping people having special interests in different archs might
try to reproduce the benchmarks that I didn't report (but did cover)
and see what happens.

> I am not suspecting you to have cherry-picked
> the best results

I'm generally very conservative when reporting *synthetic* results.
For example, the same memcached benchmark used on powerpc yielded >50%
improvement on aarch64, because the default Ubuntu Kconfig uses 64KB
base page size for powerpc but 4KB for aarch64. (Before the series,
the reclaim (swap) path takes kvm->mmu_lock for *write* on O(nr of all
pages to consider); after the series, it becomes O(actual nr of pages
to swap), which is <10% given how the benchmark was set up.)

          Ops/sec  Avg. Latency  p50 Latency  p99 Latency  p99.9 Latency
------------------------------------------------------------------------
Before  639511.40       0.09940      0.04700      0.27100       22.52700
After   974184.60       0.06471      0.04700      0.15900        3.75900

> but I'd really like to see a variety of benchmarks
> that exercise this stuff differently.

I'd be happy to try other synthetic workloads that people think that
are relatively representative. Also, I've backported the series and
started an A/B experiment involving ~1 million devices (real-world
workloads). We should have the preliminary results by the time I post
the next version.