linux-kernel - Re: [PATCH][v2] x86/kvm: Prefer native qspinlock for dedicated vCPUs irrespective of PV

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Message-ID: <175798205117.624172.7341980262867703436.b4-ty@google.com>
Date: Mon, 15 Sep 2025 17:25:33 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, pbonzini@...hat.com, vkuznets@...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, 
	lirongqing <lirongqing@...du.com>
Subject: Re: [PATCH][v2] x86/kvm: Prefer native qspinlock for dedicated vCPUs
 irrespective of PV_UNHALT

On Tue, 22 Jul 2025 19:00:05 +0800, lirongqing wrote:
> The commit b2798ba0b876 ("KVM: X86: Choose qspinlock when dedicated
> physical CPUs are available") states that when PV_DEDICATED=1
> (vCPU has dedicated pCPU), qspinlock should be preferred regardless of
> PV_UNHALT.  However, the current implementation doesn't reflect this: when
> PV_UNHALT=0, we still use virt_spin_lock() even with dedicated pCPUs.
> 
> This is suboptimal because:
> 1. Native qspinlocks should outperform virt_spin_lock() for dedicated
>    vCPUs irrespective of HALT exiting
> 2. virt_spin_lock() should only be preferred when vCPUs may be preempted
>    (non-dedicated case)
> 
> [...]

Applied to kvm-x86 guest, thanks!

[1/1] x86/kvm: Prefer native qspinlock for dedicated vCPUs irrespective of PV_UNHALT
      https://github.com/kvm-x86/linux/commit/960550503965

--
https://github.com/kvm-x86/linux/tree/next