Re: [PATCH 2/3] i386: hvf: In kick_vcpu use hv_vcpu_interrupt to force exit

[Roman Bolshakov]

On Fri, Sep 22, 2023 at 04:09:13PM +0200, Phil Dennis-Jordan wrote:
> When interrupting a vCPU thread, this patch actually tells the hypervisor to
> stop running guest code on that vCPU.
> 
> Calling hv_vcpu_interrupt actually forces a vCPU exit, analogously to
> hv_vcpus_exit on aarch64.
> 
> Previously, hvf_kick_vcpu_thread relied upon hv_vcpu_run returning very
> frequently, including many spurious exits, which made it less of a problem 
> that
> nothing was actively done to stop the vCPU thread running guest code.
> The newer, more efficient hv_vcpu_run_until exits much more rarely, so a true
> "kick" is needed.
> 

Hi Phil,

I see severe performance regression with the patch on a Windows XP
guest. The display is not refreshed properly like a broken LVDS panel,
only some horizontal lines appear on it. My test laptop for x86 hvf is
MBA 2015 with the latest Big Sur. What are you runing QEMU/HVF on?

FWIW. I recall a few years ago I submitted a similar patch that does
something similar but addresses a few more issues:
https://patchwork.kernel.org/project/qemu-devel/patch/20200729124832.79375-1-r.bolshakov@yadro.com/

I don't remember why it never got merged.

Regards,
Roman