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Re: [Qemu-devel] [PATCH net-next v3 1/3] virtio_net: propagate linkspeed


From: Jason Baron
Subject: Re: [Qemu-devel] [PATCH net-next v3 1/3] virtio_net: propagate linkspeed/duplex settings from the hypervisor
Date: Thu, 4 Jan 2018 13:12:30 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0


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 <address@hidden>
>> Cc: "Michael S. Tsirkin" <address@hidden>
>> Cc: Jason Wang <address@hidden>
>> Cc: address@hidden
>> ---
>>  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?

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



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