On Thu, Nov 24, 2016 at 09:30:49AM +0000, Kevin Traynor wrote:
On 11/24/2016 06:31 AM, Yuanhan Liu wrote:
On Tue, Nov 22, 2016 at 04:53:05PM +0200, Michael S. Tsirkin wrote:
You keep assuming that you have the VM started first and figure out things afterwards, but this does not work.
Think about a cluster of machines. You want to start a VM in a way that will ensure compatibility with all hosts in a cluster.
I see. I was more considering about the case when the dst host (including the qemu and dpdk combo) is given, and then determine whether it will be a successfull migration or not.
And you are asking that we need to know which host could be a good candidate before starting the migration. In such case, we indeed need some inputs from both the qemu and vhost-user backend.
For DPDK, I think it could be simple, just as you said, it could be either a tiny script, or even a macro defined in the source code file (we extend it every time we add a new feature) to let the libvirt to read it. Or something else.
There's the issue of APIs that tweak features as Maxime suggested.
Yes, it's a good point.
Maybe the only thing to do is to deprecate it,
Looks like so.
but I feel some way for application to pass info into guest might be benefitial.
The two APIs are just for tweaking feature bits DPDK supports before any device got connected. It's another way to disable some features (the another obvious way is to through QEMU command lines).
IMO, it's bit handy only in a case like: we have bunch of VMs. Instead of disabling something though qemu one by one, we could disable it once in DPDK.
But I doubt the useful of it. It's only used in DPDK's vhost example after all. Nor is it used in vhost pmd, neither is it used in OVS.
rte_vhost_feature_disable() is currently used in OVS, lib/netdev-dpdk.c
Hmmm. I must have checked very old code ...
netdev_dpdk_vhost_class_init(void) { static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
/* This function can be called for different classes. The initialization * needs to be done only once */ if (ovsthread_once_start(&once)) { rte_vhost_driver_callback_register(&virtio_net_device_ops); rte_vhost_feature_disable(1ULL << VIRTIO_NET_F_HOST_TSO4 | 1ULL << VIRTIO_NET_F_HOST_TSO6 | 1ULL << VIRTIO_NET_F_CSUM);
I saw the commit introduced such change, but it tells no reason why it was added. commit 362ca39639ae871806be5ae97d55e1cbb14afd92 Author: mweglicx <michalx.weglicki@intel.com> Date: Thu Apr 14 17:40:06 2016 +0100 Update relevant artifacts to add support for DPDK 16.04. Following changes are applied: - INSTALL.DPDK.md: CONFIG_RTE_BUILD_COMBINE_LIBS step has been removed because it is no longer present in DPDK configuration (combined library is created by default), - INSTALL.DPDK.md: VHost Cuse configuration is updated, - netdev-dpdk.c: Link speed definition is changed in DPDK and netdev_dpdk_get_features is updated accordingly, - netdev-dpdk.c: TSO and checksum offload has been disabled for vhostuser device. - .travis/linux-build.sh: DPDK version is updated and legacy flags have been removed in configuration. Signed-off-by: Michal Weglicki <michalx.weglicki@intel.com> Signed-off-by: Panu Matilainen <pmatilai@redhat.com> Acked-by: Daniele Di Proietto <diproiettod@vmware.com> --yliu