| Message ID | 20240506101751.3145407-1-foxywang@tencent.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: irqchip: synchronize srcu only if needed | expand |
On Mon, 06 May 2024 18:17:48 +0800, Yi Wang wrote: > 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. > > [...] Applied to kvm-x86 generic, with a lot of fixup. A sanity check on the end result would be much appreciated. Thanks! [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
On Wed, Jun 12, 2024 at 9:19 AM Sean Christopherson <seanjc@google.com> wrote: > > On Mon, 06 May 2024 18:17:48 +0800, Yi Wang wrote: > > 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. > > > > [...] > > 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
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(-)