Re: [PATCH] kvm: irqchip: Break up high order allocations of kvm_irq_routing_table

From: Paolo Bonzini
Date: Mon May 11 2015 - 07:45:43 EST

On 11/05/2015 13:25, Joerg Roedel wrote:
>> > It probably doesn't matter much indeed, but can you time the difference?
>> > kvm_set_irq_routing is not too frequent, but happens enough often that
>> > we had to use a separate SRCU instance just to speed it up (see commit
>> > 719d93cd5f5, kvm/irqchip: Speed up KVM_SET_GSI_ROUTING, 2014-01-16).
> The results vary a lot, but what I can say for sure is that the
> kvm_set_irq_routing function takes at least twice as long (~10.000 vs
> ~22.000 cycles) as before on my AMD Kaveri machine (maximum was between
> 3-4 times as long).
> On the other side this function is only called 2 times at boot in my
> test, so I couldn't detect a noticable effect on the overall boot time
> of the guest (37 disks were attached).

Christian, can you test this?

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