Il 12/05/2014 11:28, Gonglei (Arei) ha scritto:
From previous discussion:
https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg04925.html
we know that you are going to replace RCU in KVM_SET_GSI_ROUTING with SRCU.
Though
SRCU is quite better than originally RCU, in our test case this cannot satisfy
our needs. Our VMs
work in telecom scenario, VMs report CPU and memory usage to balance node each
second, and
balance node dispatch works to different VMs according to VM load. Since this
balance needs
high accuracy, IRQ affinity settings in VM also need high accuracy, so we
balance IRQ affinity in
every 0.5s. So for telecom scenario, KVM_SET_GSI_ROUTING IOCTL needs much
optimization.
And in live migration case, VHOST_SET_MEM_TABLE needs attention.
We tried to change synchronize_rcu() to call_rcu() with rate limit, but rate
limit is not easy to
configure. Do you have better ideas to achieve this? Thanks.
Perhaps we can check for cases where only the address is changing, and
poke at an existing struct kvm_kernel_irq_routing_entry without doing
any RCU synchronization?
As long as kvm_set_msi_irq only reads address_lo once, it should work.
VHOST_SET_MEM_TABLE is a different problem. What happens in userspace
that leads to calling that ioctl? Can we remove it altogether, or delay
it to after the destination has started running?
Paolo
