Re: [Xen-devel] [PATCH RFC v3 0/6] x86/idle: add halt poll support

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Nov 13, 2017 at 06:05:59PM +0800, Quan Xu wrote:
> From: Yang Zhang <yang.zhang.wz@xxxxxxxxx>
> 
> Some latency-intensive workload have seen obviously performance
> drop when running inside VM. The main reason is that the overhead
> is amplified when running inside VM. The most cost I have seen is
> inside idle path.

Meaning an VMEXIT b/c it is an 'halt' operation ? And then going
back in guest (VMRESUME) takes time. And hence your latency gets
all whacked b/c of this?

So if I understand - you want to use your _full_ timeslice (of the guest)
without ever (or as much as possible) to go in the hypervisor?

Which means in effect you don't care about power-saving or CPUfreq
savings, you just want to eat the full CPU for snack?

> 
> This patch introduces a new mechanism to poll for a while before
> entering idle state. If schedule is needed during poll, then we
> don't need to goes through the heavy overhead path.

Schedule of what? The guest or the host?


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