From: Yi Wang <up2wing@gmail.com>
To: 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,
borntraeger@linux.ibm.com, frankja@linux.ibm.com,
imbrenda@linux.ibm.com, weijiang.yang@intel.com
Cc: up2wing@gmail.com
Subject: [v5 0/3] KVM: irqchip: synchronize srcu only if needed
Date: Mon, 6 May 2024 18:17:48 +0800 [thread overview]
Message-ID: <20240506101751.3145407-1-foxywang@tencent.com> (raw)
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 this patch has not been tested
thoroughly on s390 platform. Thanks to Christian for a quick test on
s390 and it still seems to work[1].
Changelog:
----------
v5:
- rename new function to kvm_init_irq_routing as Sean suggested.
- move invok of function of setting up empty before kvm_arch_init_vm.
- Add necessary comment.
v4:
- replace loop with memset when setup empty irq routing table.
v3:
- squash setup empty routing function and use of that into one commit
- drop the comment in s390 part
v2:
- setup empty irq routing in kvm_create_vm
- don't setup irq routing in x86 KVM_CAP_SPLIT_IRQCHIP
- don't setup irq routing in s390 KVM_CREATE_IRQCHIP
v1:
https://lore.kernel.org/kvm/20240112091128.3868059-1-foxywang@tencent.com/
1. https://lore.kernel.org/lkml/f898e36f-ba02-4c52-a3be-06caac13323e@linux.ibm.com/
Yi Wang (3):
KVM: setup empty irq routing when create vm
KVM: x86: don't setup empty irq routing when KVM_CAP_SPLIT_IRQCHIP
KVM: s390: don't setup dummy routing when KVM_CREATE_IRQCHIP
arch/s390/kvm/kvm-s390.c | 9 +--------
arch/x86/kvm/irq.h | 1 -
arch/x86/kvm/irq_comm.c | 5 -----
arch/x86/kvm/x86.c | 3 ---
include/linux/kvm_host.h | 2 ++
virt/kvm/irqchip.c | 23 +++++++++++++++++++++++
virt/kvm/kvm_main.c | 9 ++++++++-
7 files changed, 34 insertions(+), 18 deletions(-)
--
2.39.3
next reply other threads:[~2024-05-06 10:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-06 10:17 Yi Wang [this message]
2024-05-06 10:17 ` [v5 1/3] KVM: setup empty irq routing when create vm Yi Wang
2024-05-06 11:41 ` Christian Borntraeger
2024-05-06 10:17 ` [v5 2/3] KVM: x86: don't setup empty irq routing when KVM_CAP_SPLIT_IRQCHIP Yi Wang
2024-05-06 10:17 ` [v5 3/3] KVM: s390: don't setup dummy routing when KVM_CREATE_IRQCHIP Yi Wang
2024-05-06 11:42 ` Christian Borntraeger
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