Il 24/02/2014 12:58, Christian Borntraeger ha scritto:
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 userspace 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.
By changing the code to use a private srcu we can speed things up.
This patch reduces the boot time till mounting root from 8 to 2
seconds on my s390 guest with 100 disks.
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
v1-v2: Fix missing hunk in kvm_irq_has_notifier. This was unnoticed on
s390, as our code did not use it.
In fact, there are other accesses to irq_routing elsewhere in virt/kvm
which should be changed to irq_srcu (which in turn probably means that
it's better to make the SRCU instance per-VM).
My fault, I should have delayed the patch to after the merge window
instead of doing a shoddy review. I'll test the complete patch myself
since VFIO is probably the only thing that can cover it 100%, and s390
doesn't do VFIO.
Paolo
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