| Message ID | 20240121111730.262429-1-foxywang@tencent.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: irqchip: synchronize srcu only if needed | expand |
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.
On Wed, Jan 24, 2024 at 8:14 PM Christian Borntraeger <borntraeger@linux.ibm.com> wrote: > > 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. Thanks very much, Christian! --- Best wishes 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. Changelog: ---------- v1->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/ Yi Wang (4): KVM: irqchip: add setup empty irq routing function 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 | 13 +++++-------- arch/x86/kvm/irq.h | 1 - arch/x86/kvm/irq_comm.c | 5 ----- arch/x86/kvm/x86.c | 3 --- include/linux/kvm_host.h | 1 + virt/kvm/irqchip.c | 19 +++++++++++++++++++ virt/kvm/kvm_main.c | 4 ++++ 7 files changed, 29 insertions(+), 17 deletions(-)