Messages in this thread | | | Date | Thu, 21 Dec 2017 02:10:38 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH net-next 1/2] virtio_net: allow hypervisor to indicate linkspeed and duplex setting |
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On Wed, Dec 20, 2017 at 04:32:52PM -0500, Jason Baron wrote: > > > On 12/20/2017 12:52 PM, Michael S. Tsirkin wrote: > > On Wed, Dec 20, 2017 at 12:07:55PM -0500, Jason Baron wrote: > >> > >> > >> On 12/20/2017 09:57 AM, Michael S. Tsirkin wrote: > >>> On Thu, Dec 14, 2017 at 02:33:53PM -0500, Jason Baron wrote: > >>>> If the hypervisor exports the link and duplex speed, let's use that instead > >>>> of the default unknown speed. The user can still overwrite it later if > >>>> desired via: 'ethtool -s'. This allows the hypervisor to set the default > >>>> link speed and duplex setting without requiring guest changes and is > >>>> consistent with how other network drivers operate. We ran into some cases > >>>> where the guest software was failing due to a lack of linkspeed and had to > >>>> fall back to a fully emulated network device that does export a linkspeed > >>>> and duplex setting. > >>>> > >>>> Implement by adding a new VIRTIO_NET_F_SPEED_DUPLEX feature flag, to > >>>> indicate that a linkspeed and duplex setting are present. > >>>> > >>>> Signed-off-by: Jason Baron <jbaron@akamai.com> > >>>> Cc: "Michael S. Tsirkin" <mst@redhat.com> > >>>> Cc: Jason Wang <jasowang@redhat.com> > >>>> --- > >>>> drivers/net/virtio_net.c | 11 ++++++++++- > >>>> include/uapi/linux/virtio_net.h | 4 ++++ > >>>> 2 files changed, 14 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > >>>> index 6fb7b65..e7a2ad6 100644 > >>>> --- a/drivers/net/virtio_net.c > >>>> +++ b/drivers/net/virtio_net.c > >>>> @@ -2671,6 +2671,14 @@ static int virtnet_probe(struct virtio_device *vdev) > >>>> netif_set_real_num_rx_queues(dev, vi->curr_queue_pairs); > >>>> > >>>> virtnet_init_settings(dev); > >>>> + if (virtio_has_feature(vdev, VIRTIO_NET_F_SPEED_DUPLEX)) { > >>>> + vi->speed = virtio_cread32(vdev, > >>>> + offsetof(struct virtio_net_config, > >>>> + speed)); > >>>> + vi->duplex = virtio_cread8(vdev, > >>>> + offsetof(struct virtio_net_config, > >>>> + duplex)); > >>>> + } > >>>> > >>>> err = register_netdev(dev); > >>>> if (err) { > >>> > >>> How are we going to validate speed values? Imagine host > >>> using a new 1000Gbit device and exposing that to guest. > >>> > >>> Need to think what do we want guest to do. > >>> I think that ideally we'd say it's a 100Gbit device. > >>> > >>> For duplex, force to one of 3 valid values? > >> > >> So I didn't provide validation here b/c as you point out its not clear > >> how we would validate it. I don't believe h/w drivers do any validation > >> here either. > > > > Right but hardware tends not to change as quickly as the hypervisors :) > > For virtual device drivers, we need some way to handle forward > > compatibility since hypervisors do change quite quickly. > > > >> They simply propagate the value from the the underlying > >> device. So that seemed reasonable to me. > >> > >> Why do you divide by 10 in the above example? Would you propose always > >> dividing what the device reports by 10? > > > > No, that was just an example. I was just suggesting rounding down to > > next valid known speed. > > I see, but virtio currently uses ethtool_validate_speed() which allows > arbitrary values up to INT_MAX in units of Mbps. That seems to leave > plenty of headroom. So I could use that function for validation as well > as well as ethtool_validate_duplex() and if they fail fall back to > SPEED_UNKNOWN and DUPLEX_UNKNOWN?
Sounds good.
> > > >>> > >>> > >>>> @@ -2796,7 +2804,8 @@ static struct virtio_device_id id_table[] = { > >>>> VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN, \ > >>>> VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \ > >>>> VIRTIO_NET_F_CTRL_MAC_ADDR, \ > >>>> - VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS > >>>> + VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \ > >>>> + VIRTIO_NET_F_SPEED_DUPLEX > >>>> > >>>> static unsigned int features[] = { > >>>> VIRTNET_FEATURES, > >>>> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h > >>>> index fc353b5..acfcf68 100644 > >>>> --- a/include/uapi/linux/virtio_net.h > >>>> +++ b/include/uapi/linux/virtio_net.h > >>>> @@ -36,6 +36,7 @@ > >>>> #define VIRTIO_NET_F_GUEST_CSUM 1 /* Guest handles pkts w/ partial csum */ > >>>> #define VIRTIO_NET_F_CTRL_GUEST_OFFLOADS 2 /* Dynamic offload configuration. */ > >>>> #define VIRTIO_NET_F_MTU 3 /* Initial MTU advice */ > >>>> +#define VIRTIO_NET_F_SPEED_DUPLEX 4 /* Host set linkspeed and duplex */ > >>>> #define VIRTIO_NET_F_MAC 5 /* Host has given MAC address. */ > >>>> #define VIRTIO_NET_F_GUEST_TSO4 7 /* Guest can handle TSOv4 in. */ > >>>> #define VIRTIO_NET_F_GUEST_TSO6 8 /* Guest can handle TSOv6 in. */ > >>> > >>> I think I'd prefer a high feature bit - low bits are ones that can > >>> be backported to legacy interfaces, so I think we should hang on to > >>> these for fixing issues that break communication completely (like the > >>> mtu). > >>> > >> > >> So I went with a low bit here b/c in the virtio spec 'section 2.2 > >> Feature Bits': > >> > >> > >> 0 to 23 > >> Feature bits for the specific device type > >> 24 to 32 > >> Feature bits reserved for extensions to the queue and feature > >> negotiation mechanisms > >> 33 and above > >> Feature bits reserved for future extensions. > >> > >> So virtio_net already goes up to 23 (but omits 4 and 6), and I wasn't > >> sure if it was reasonable to use the higher bits. It looks like the code > >> would handle the higher bits ok, so I can try that - bit 33 perhaps ? > >> > >> Thanks, > >> > >> -Jason > > > > > > Transports started from bit 24 and are growing up. > > So I would say devices should start from bit 63 and grow down. > > > > Ok, I will use 63. > > Thanks, > > -Jason >
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