lkml.org 
[lkml]   [2024]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Subject[v4 RESEND 0/3] KVM: irqchip: synchronize srcu only if needed
Date
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:
----------
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 | 1 +
virt/kvm/irqchip.c | 19 +++++++++++++++++++
virt/kvm/kvm_main.c | 4 ++++
7 files changed, 25 insertions(+), 17 deletions(-)

--
2.39.3


\
 
 \ /
  Last update: 2024-05-27 18:04    [W:0.396 / U:0.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site