Il 16/01/2014 21:22, Michael S. Tsirkin ha scritto: >> [PATCHv3] kvm/irqchip: Speed up KVM_SET_GSI_ROUTING >> >> When starting lots of dataplane devices the bootup takes very long >> on my s390 system(prototype irqfd code). With larger setups we are even >> able to trigger some timeouts in some components. >> Turns out that the KVM_SET_GSI_ROUTING ioctl takes very >> long (strace claims up to 0.1 sec) when having multiple CPUs. >> This is caused by the synchronize_rcu and the HZ=100 of s390. >> >> Lets use the expedited variant to speed things up as suggested by >> Michael S. Tsirkin >> >> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> >> --- >> virt/kvm/irqchip.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c >> index 20dc9e4..dbcfde7 100644 >> --- a/virt/kvm/irqchip.c >> +++ b/virt/kvm/irqchip.c >> @@ -226,7 +226,7 @@ int kvm_set_irq_routing(struct kvm *kvm, >> kvm_irq_routing_update(kvm, new); >> mutex_unlock(&kvm->irq_lock); >> >> - synchronize_rcu(); >> + synchronize_rcu_expedited(); >> >> new = old; >> r = 0; > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Well... I love to contradict myself, so: no way this can be accepted this close to the end of the merge window. :( synchronize_rcu_expedited() forces a context switch on all CPUs, even those that are not running KVM. Thus, this patch might help a guest DoS its host by changing the IRQ routing tables in a loop. So this will have to wait for 3.15. We have ~2 months to do performance measurements on the v2 patch. Sorry. Thanks, Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
