Re: [PATCH net-next v3 1/3] virtio_net: propagate linkspeed/duplex settings from the hypervisor

[Jason Baron <jbaron@akamai.com>]

On 01/04/2018 01:22 PM, Michael S. Tsirkin wrote:
> On Thu, Jan 04, 2018 at 01:12:30PM -0500, Jason Baron wrote:
>>
>>
>> On 01/04/2018 12:05 PM, Michael S. Tsirkin wrote:
>>> On Thu, Jan 04, 2018 at 12:16:44AM -0500, Jason Baron wrote:
>>>> The ability to set speed and duplex for virtio_net is useful in various
>>>> scenarios as described here:
>>>>
>>>> 16032be virtio_net: add ethtool support for set and get of settings
>>>>
>>>> However, it would be nice to be able to set this from the hypervisor,
>>>> such that virtio_net doesn't require custom guest ethtool commands.
>>>>
>>>> Introduce a new feature flag, VIRTIO_NET_F_SPEED_DUPLEX, which allows
>>>> the hypervisor to export a linkspeed and duplex setting. The user can
>>>> subsequently overwrite it later if desired via: 'ethtool -s'.
>>>>
>>>> Note that VIRTIO_NET_F_SPEED_DUPLEX is defined as bit 63, the intention
>>>> is that device feature bits are to grow down from bit 63, since the
>>>> transports are starting from bit 24 and growing up.
>>>>
>>>> Signed-off-by: Jason Baron <jbaron@akamai.com>
>>>> Cc: "Michael S. Tsirkin" <mst@redhat.com>
>>>> Cc: Jason Wang <jasowang@redhat.com>
>>>> Cc: virtio-dev@lists.oasis-open.org
>>>> ---
>>>>  drivers/net/virtio_net.c        | 19 ++++++++++++++++++-
>>>>  include/uapi/linux/virtio_net.h | 13 +++++++++++++
>>>>  2 files changed, 31 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>>> index 6fb7b65..0b2d314 100644
>>>> --- a/drivers/net/virtio_net.c
>>>> +++ b/drivers/net/virtio_net.c
>>>> @@ -2146,6 +2146,22 @@ static void virtnet_config_changed_work(struct work_struct *work)
>>>>  
>>>>  	vi->status = v;
>>>>  
>>>> +	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_SPEED_DUPLEX)) {
>>>
>>> BTW we can avoid this read for when link goes down.
>>> Not a big deal but still.
>>
>> So you are saying that we can just set vi->speed and vi->duplex to
>> 'unknown' when the link goes down and not check for the presence of
>> VIRTIO_NET_F_SPEED_DUPLEX?
>>
>> If so, that could over-write what the user may have configured in the
>> guest via 'ethtool -s' when the link goes down, so that would be a
>> change in behavior, but perhaps that is ok?
> 
> No - what I am saying is that your patch overwrites the values
> set by user when link goes down.
> 
> I suggest limiting this call to when
> 
> if (vi->status & VIRTIO_NET_S_LINK_UP)
> 
> and then the values are overwritten when link goes up
> which seems closer to what a user might expect.
ok, will update this for v4.

Thanks,

-Jason

> 
>>
>> I think I would prefer to have the link down event still check for
>> VIRTIO_NET_F_SPEED_DUPLEX before changing speed/duplex. That way we
>> still have 2 modes for updating the fields:
>>
>> 1) completely guest controlled. Same as we have now and host does not
>> change any values and does not set VIRTIO_NET_F_SPEED_DUPLEX flag (hence
>> don't remove above check).
>>
>> 2) if speed or duplex or speed is set in the qemu command line, then set
>> the VIRTIO_NET_F_SPEED_DUPLEX and have host control the settings of
>> speed/duplex (with ability of guest to over-write if it wanted to).
>>
>>
>>>
>>>> +		u32 speed;
>>>> +		u8 duplex;
>>>> +
>>>> +		speed = virtio_cread32(vi->vdev,
>>>> +				       offsetof(struct virtio_net_config,
>>>> +						speed));
>>>> +		if (ethtool_validate_speed(speed))
>>>> +			vi->speed = speed;
>>>> +		duplex = virtio_cread8(vi->vdev,
>>>> +				       offsetof(struct virtio_net_config,
>>>> +						duplex));
>>>> +		if (ethtool_validate_duplex(duplex))
>>>> +			vi->duplex = duplex;
>>>> +	}
>>>> +
>>>>  	if (vi->status & VIRTIO_NET_S_LINK_UP) {
>>>>  		netif_carrier_on(vi->dev);
>>>>  		netif_tx_wake_all_queues(vi->dev);
>>>
>>> OK so this handles the case when VIRTIO_NET_F_STATUS is set,
>>> but when it's clear we need to call this from virtnet_probe.
>>>
>>> I propose moving this chunk to a function and calling from two places.
>>>
>>
>> good point. will update.
>>
>> Thanks,
>>
>> -Jason
>>
>>>
>>>> @@ -2796,7 +2812,8 @@ 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..5de6ed3 100644
>>>> --- a/include/uapi/linux/virtio_net.h
>>>> +++ b/include/uapi/linux/virtio_net.h
>>>> @@ -57,6 +57,8 @@
>>>>  					 * Steering */
>>>>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
>>>>  
>>>> +#define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Device set linkspeed and duplex */
>>>> +
>>>>  #ifndef VIRTIO_NET_NO_LEGACY
>>>>  #define VIRTIO_NET_F_GSO	6	/* Host handles pkts w/ any GSO type */
>>>>  #endif /* VIRTIO_NET_NO_LEGACY */
>>>> @@ -76,6 +78,17 @@ struct virtio_net_config {
>>>>  	__u16 max_virtqueue_pairs;
>>>>  	/* Default maximum transmit unit advice */
>>>>  	__u16 mtu;
>>>> +	/*
>>>> +	 * speed, in units of 1Mb. All values 0 to INT_MAX are legal.
>>>> +	 * Any other value stands for unknown.
>>>> +	 */
>>>> +	__u32 speed;
>>>> +	/*
>>>> +	 * 0x00 - half duplex
>>>> +	 * 0x01 - full duplex
>>>> +	 * Any other value stands for unknown.
>>>> +	 */
>>>> +	__u8 duplex;
>>>>  } __attribute__((packed));
>>>>  
>>>>  /*
>>>> -- 
>>>> 2.6.1