From: Christian Borntraeger <borntraeger@linux.ibm.com>
To: Yi Wang <up2wing@gmail.com>,
seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, wanpengli@tencent.com,
foxywang@tencent.com, oliver.upton@linux.dev, maz@kernel.org,
anup@brainfault.org, atishp@atishpatra.org,
frankja@linux.ibm.com, imbrenda@linux.ibm.com
Subject: Re: [v2 0/4] KVM: irqchip: synchronize srcu only if needed
Date: Wed, 24 Jan 2024 13:14:40 +0100 [thread overview]
Message-ID: <f898e36f-ba02-4c52-a3be-06caac13323e@linux.ibm.com> (raw)
In-Reply-To: <20240121111730.262429-1-foxywang@tencent.com>
Am 21.01.24 um 12:17 schrieb Yi Wang:
> From: Yi Wang <foxywang@tencent.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.
>
> Note: I have no s390 machine so the s390 patch has not been tested.
I just did a quick sniff and it still seems to work. No performance check etc.
next prev parent reply other threads:[~2024-01-24 12:15 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-21 11:17 [v2 0/4] KVM: irqchip: synchronize srcu only if needed Yi Wang
2024-01-21 11:17 ` [v2 1/4] KVM: irqchip: add setup empty irq routing function Yi Wang
2024-01-23 18:47 ` Oliver Upton
2024-01-24 2:12 ` Yi Wang
2024-01-21 11:17 ` [v2 2/4] KVM: setup empty irq routing when create vm Yi Wang
2024-01-21 11:17 ` [v2 3/4] KVM: x86: don't setup empty irq routing when KVM_CAP_SPLIT_IRQCHIP Yi Wang
2024-01-21 11:17 ` [v2 4/4] KVM: s390: don't setup dummy routing when KVM_CREATE_IRQCHIP Yi Wang
2024-01-23 18:54 ` Oliver Upton
2024-01-24 2:16 ` Yi Wang
2024-01-24 12:14 ` Christian Borntraeger [this message]
2024-01-24 12:44 ` [v2 0/4] KVM: irqchip: synchronize srcu only if needed Yi Wang
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