Re: [Qemu-devel] [PATCH v2 0/3] virtio: proposal to optimize accesses to VQs

[Paolo Bonzini]

On 16/12/2015 10:28, Vincenzo Maffione wrote:
> Assuming my TX experiments with disconnected backend (and I disable
> CPU dynamic scaling of performance, etc.):
>   1) after patch 1 and 2, virtio bottleneck jumps from ~1Mpps to 1.910 Mpps.
>   2) after patch 1,2 and 3, virtio bottleneck jumps to 2.039 Mpps.
> 
> So I see an improvement for patch 3, and I guess it's because we avoid
> an additional memory translation and related overhead. I believe that
> avoiding the memory translation is more beneficial than avoiding the
> variable-sized memcpy.
> I'm not surprised of that, because taking a brief look at what happens
> under the hood when you call an access_memory() function - it looks
> like a lot of operations.

Great, thanks for confirming!

Paolo