From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefan Hajnoczi <stefanha@gmail.com>
Subject: Re: [Qemu-devel] Why I advise against using ivshmem
Date: Wed, 18 Jun 2014 18:51:20 +0800
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To: David Marchand <david.marchand@6wind.com>
Cc: Henning Schild <henning.schild@siemens.com>, Olivier MATZ <olivier.matz@6wind.com>, kvm <kvm@vger.kernel.org>, qemu-devel <qemu-devel@nongnu.org>, Linux Virtualization <virtualization@lists.linux-foundation.org>, Paolo Bonzini <pbonzini@redhat.com>, Vincent JARDIN <vincent.jardin@6wind.com>, "thomas.monjalon@6wind.com" <thomas.monjalon@6wind.com>
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On Tue, Jun 17, 2014 at 11:03:32AM +0200, David Marchand wrote:
> On 06/17/2014 04:54 AM, Stefan Hajnoczi wrote:
> >ivshmem has a performance disadvantage for guest-to-host
> >communication.  Since the shared memory is exposed as PCI BARs, the
> >guest has to memcpy into the shared memory.
> >
> >vhost-user can access guest memory directly and avoid the copy inside th=
e guest.
>=20
> Actually, you can avoid this memory copy using frameworks like DPDK.

I guess it's careful to allocate all packets in the mmapped BAR?

That's fine if you can modify applications but doesn't work for
unmodified applications using regular networking APIs.

Stefan

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