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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Wed, 16 Dec 2015 10:34:06 +0100
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Subject: Re: [Qemu-devel] [PATCH v2 0/3] virtio: proposal to optimize
	accesses to VQs
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To: Vincenzo Maffione <v.maffione@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Markus Armbruster <armbru@redhat.com>, Giuseppe Lettieri <g.lettieri@iet.unipi.it>, Luigi Rizzo <rizzo@iet.unipi.it>



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