Re: [PATCH v8 00/10] VMSCAPE optimization for BHI variant

Pawan Gupta
2026-03-30T16:11:09Z

On Mon, Mar 30, 2026 at 03:16:32AM +0000, Jon Kohler wrote:
> Tested the v7 of this series with 6.18.y and one of our performance
> suites, where we had previously bisected a significant regression to
> the enablement of the VMSCAPE mitigation. This particular suite looks
> at synthetic performance using KVM virtualized Windows guests.
>
> Long story short, this suite tries to derive what end user experience
> would be in these virtual machines while performing a standardized set
> of synthetic tasks on real apps.
>
> VMSCAPE hits especially hard when enabling Windows HVCI, which drives
> a much higher VMExit count, all else equals.
>
> Tested on an Intel Xeon 6444Y (SPR)
>
> TLDR, we're really happy with the results. The following was with
> Intel MBEC *enabled*, so even with that speedup (and drastic reduction
> in VMExits), this optimization makes a significant difference.
>
> - CPU‑ready time drops ~70 % across all steady‑state and log‑on metrics
> with this series, indicating more efficient context switching even
> though overall hypervisor CPU rises ~14 % (steady) to ~12 % (max).
> Basically, we're getting more actual work done.
> - Read/write IOPS increase by ~18–37 % and 14–20 % respectively, while
> average IO latency remains largely unchanged or slightly lower in
> steady metrics.
> - Power consumption falls 5–11 % in every category
> - Login times improve by 4–6 % on average.
> - Application start‑up times are generally better (Word, Excel,
> PowerPoint, Outlook), especially Outlook max time drops 67 %, a clear
> win for end‑user experience.

These results are promising.

> Tested-By: Jon Kohler <jon@nutanix.com>

Thanks for testing, Jon.