Re: [PATCH 6/8] x86: KVM guest: hypercall batching

[Avi Kivity <avi@qumranet.com>]

Zhao Forrest wrote:
> Hi Avi,
>
> After reading the patch, I think the hypercall batching mechanism is as follows:
> 1 defer the MMU-related operations and buffer them in
> kvm_para_state->mmu_queue[]
> 2 during the flush period, kvm_mmu_op() is called to flush operations
> in kvm_para_state->mmu_queue[]
> 3 kvm_mmu_op() generate a hypercall for each operation in
> kvm_para_state->mmu_queue[]; thus trigger a context switch from guest
> mode to kernel mode for each operation.
>
> My question is: Is it possible to only generate a single
> hypercall(thus a single context switch) for all buffered MMU
> operations in kvm_para_state->mmu_queue[]? This way we could further
> reduce overhead, am I right?
> BTW. I don't have a deep understanding of KVM. So this is just a
> question out of my curiosity.
>
>   

mmu_queue_flush() is called once per batch, so we only have one 
hypercall per batch (at least if the data doesn't exceed 512 bytes).

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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