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[Qemu-devel] [PATCH 00/19 v2] Add virtio-net/tap support for partial csu
From: |
Mark McLoughlin |
Subject: |
[Qemu-devel] [PATCH 00/19 v2] Add virtio-net/tap support for partial csums and GSO |
Date: |
Thu, 22 Oct 2009 17:43:31 +0100 |
Hey,
Over a year ago we added some code to qemu-kvm.git which takes
advantage of the recent tun/tap IFF_VNET_HDR feature in order to allow
virtio-net to send and receive packets with partial checksums and
segmentation offloaded:
http://article.gmane.org/gmane.comp.emulators.kvm.devel/20440
"This allows us to pass larger packets and packets with
partial checkums between the guest and the host, greatly
increasing the achievable bandwidth."
Unfortunately, that implementation was quite hacky as it
made some assumptions that would break if e.g. you added another
network client to a vlan where the feature had enabled.
Now that we have the -netdev parameter, we can more safely
pair the NIC and backend, allowing us to negatiate features like
this.
What follows is a somewhat cleaned up version of the code
from qemu-kvm.git. Further cleanups are probably possible, but I
think this much is mergeable. Some points of discussion:
- If you start a guest on a host which supports IFF_VNET_HDR and
migrate to a host which doesn't support it, we can't just tell
the guest to stop using GSO.
We need prevent this by rejecting the migration on the destination
if IFF_VNET_HDR is required but not available. However, in my
testing if a load() function returns an error, the migration is
seen to have completed on the source but failed on the destination.
Clearly that's wrong, but I haven't investigated further yet.
Also, we provide a vnet_hdr= arg so that people can prevent the
feature being used on the source or require that is available on
the destination.
- I've slightly abused QemuOpts in 05/19. Comments welcome.
- The whole mess around adding a 'raw' packet flag for the gratuitous
ARP packet is gratuitously messy.
- I'm always enabling IFF_VNET_HDR if it's available. I don't think
that's a problem, especially compared to what would be required to
only selectively enable it.
Changes since v1:
- add has_vnet_hdr and has_ufo fields for ease of vmstate conversion
- use qemu_error() in virtio_net_load()
Cheers,
Mark.
- [Qemu-devel] [PATCH 00/19 v2] Add virtio-net/tap support for partial csums and GSO,
Mark McLoughlin <=
- [Qemu-devel] [PATCH 01/19] net: remove unused includes of if_tun.h and if_tap.h, Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 04/19] net: enable IFF_VNET_HDR on tap fds if available, Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 13/19] net: implement tap support for receive_raw(), Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 07/19] net: add a client type code, Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 02/19] net: import linux tap ioctl definitions, Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 03/19] net: make tap_receive() re-use tap_receive_iov() code, Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 08/19] net: add tap_has_vnet_hdr() and tap_using_vnet_hdr() APIs, Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 10/19] net: add an API for 'raw' packets, Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 05/19] net: refactor tap initialization, Mark McLoughlin, 2009/10/22
- [Qemu-devel] [PATCH 14/19] virtio-net: add vnet_hdr support, Mark McLoughlin, 2009/10/22