linux-kernel - Re: [v5 0/3] KVM: irqchip: synchronize srcu only if needed

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Date: Wed, 12 Jun 2024 21:16:18 +0800
From: Yi Wang <up2wing@...il.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, wanpengli@...cent.com, 
	foxywang@...cent.com, oliver.upton@...ux.dev, maz@...nel.org, 
	anup@...infault.org, atishp@...shpatra.org, borntraeger@...ux.ibm.com, 
	frankja@...ux.ibm.com, imbrenda@...ux.ibm.com, weijiang.yang@...el.com
Subject: Re: [v5 0/3] KVM: irqchip: synchronize srcu only if needed

On Wed, Jun 12, 2024 at 9:19 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Mon, 06 May 2024 18:17:48 +0800, Yi Wang wrote:
> > From: Yi Wang <foxywang@...cent.com>
> >
> > We found that it may cost more than 20 milliseconds very accidentally
> > to enable cap of KVM_CAP_SPLIT_IRQCHIP on a host which has many vms
> > already.
> >
> > The reason is that when vmm(qemu/CloudHypervisor) invokes
> > KVM_CAP_SPLIT_IRQCHIP kvm will call synchronize_srcu_expedited() and
> > might_sleep and kworker of srcu may cost some delay during this period.
> > One way makes sence is setup empty irq routing when creating vm and
> > so that x86/s390 don't need to setup empty/dummy irq routing.
> >
> > [...]
>
> Applied to kvm-x86 generic, with a lot of fixup.  A sanity check on the end
> result would be much appreciated.  Thanks!

The code LGTM. I did some tests in my Intel machine and found no problems.

Thanks for your work :)

>
> [1/3] KVM: Setup empty IRQ routing when creating a VM
>       https://github.com/kvm-x86/linux/commit/fbe4a7e881d4
> [2/3] KVM: x86: Don't re-setup empty IRQ routing when KVM_CAP_SPLIT_IRQCHIP
>       https://github.com/kvm-x86/linux/commit/e3c89f5dd11d
> [3/3] KVM: s390: Don't re-setup dummy routing when KVM_CREATE_IRQCHIP
>       https://github.com/kvm-x86/linux/commit/c4201bd24f4a
>
> --
> https://github.com/kvm-x86/linux/tree/next




---
Best wishes
Yi Wang