RE: [RFC PATCH v6 6/6] KVM: selftests: Add tests for VM and vCPU cap KVM_CAP_X86_DISABLE_EXITS

[Kechen Lu]

Hi Zhi,

> -----Original Message-----
> From: Zhi Wang <zhi.wang.linux@xxxxxxxxx>
> Sent: Thursday, February 2, 2023 7:09 AM
> To: Kechen Lu <kechenl@xxxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx; seanjc@xxxxxxxxxx; pbonzini@xxxxxxxxxx;
> chao.gao@xxxxxxxxx; shaoqin.huang@xxxxxxxxx; vkuznets@xxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [RFC PATCH v6 6/6] KVM: selftests: Add tests for VM and vCPU
> cap KVM_CAP_X86_DISABLE_EXITS
> 
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> 
> On Sat, 21 Jan 2023 02:07:38 +0000
> Kechen Lu <kechenl@xxxxxxxxxx> wrote:
> 
> It works on my box now. LGTM. I was curious if there is any other userspace
> application using this? It would be interesting to see their strategies.
> 
Thanks for testing this! Appreciated. 

For userspace applications, we had a POC with the changes in QEMU, to do the static per-vCPU HLT disabling, depending on the users to have the flexibility run guest workloads on these none-hlt-exits vCPUs instead of disabling hlt exits for whole VM, we saw 3%+ performance benefits. Furthermore, we had the dynamically toggled hlt exits strategy applied on QEMU, which depending on the guest stats and heuristics to do the hlt exits toggling.

BR,
Kechen