[dpdk-dev] [PATCH v6] net/virtio: add set_mtu in virtio

Yuanhan Liu yuanhan.liu at linux.intel.com
Wed Sep 28 01:11:59 CEST 2016


On Tue, Sep 27, 2016 at 08:44:20PM +0000, Dey, Souvik wrote:
> Hi Stephen, 
> 	So what should be my next steps , should I submit a v7 for this patch or you suggest otherwise.

Yes, please. Another note is please don't use white space for
indentation, use TAB instead.

	-yliu
> 
> --
> Regards,
> Souvik
> 
> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen at networkplumber.org] 
> Sent: Tuesday, September 27, 2016 2:57 PM
> To: Dey, Souvik <sodey at sonusnet.com>
> Cc: Kavanagh, Mark B <mark.b.kavanagh at intel.com>; Yuanhan Liu <yuanhan.liu at linux.intel.com>; dev at dpdk.org
> Subject: Re: [PATCH v6] net/virtio: add set_mtu in virtio
> 
> On Fri, 23 Sep 2016 15:17:37 +0000
> "Dey, Souvik" <sodey at sonusnet.com> wrote:
> 
> > Hi Liu/Mark/Stephen,
> > 
> >               I have tried to modify the code with all of your latest comments. Do let me know if this looks fine or you have more comments.
> > 
> > 
> > 
> > Changes done :
> > 
> > -- max frame ize is compare to VIRTIO_MAX_RX_PKTLEN instead of 
> > dev_info.max_rx_pktlen
> > 
> > -- removed the CRC_LEN from the ether_len calculation and added the 
> > merge rx buf hdr len. ether_hdr_len = ETHER_HDR_LEN + VLAN_TAG_SIZE + 
> > hw->vtnet_hdr_size
> > 
> > -- Still retained the VLAN Size as the worst case scenario.
> > 
> > 
> > 
> > 
> > 
> > --
> > 
> > drivers/net/virtio/virtio_ethdev.c | 16 ++++++++++++++++
> > 
> > 1 file changed, 16 insertions(+)
> > 
> > 
> > 
> > diff --git a/drivers/net/virtio/virtio_ethdev.c 
> > b/drivers/net/virtio/virtio_ethdev.c
> > 
> > index 423c597..1dbfea6 100644
> > 
> > --- a/drivers/net/virtio/virtio_ethdev.c
> > 
> > +++ b/drivers/net/virtio/virtio_ethdev.c
> > 
> > @@ -653,12 +653,20 @@ virtio_dev_allmulticast_disable(struct 
> > rte_eth_dev *dev)
> > 
> >                 PMD_INIT_LOG(ERR, "Failed to disable allmulticast");
> > 
> > }
> > 
> > 
> > 
> > +#define VLAN_TAG_SIZE           4    /* 802.3ac tag (not DMA'd) */
> > 
> > +
> > 
> > +static int virtio_mtu_set(struct rte_eth_dev *dev, uint16_t mtu)
> > 
> > +{
> > 
> > +            struct virtio_hw *hw = dev->data->dev_private;
> > 
> > +            uint32_t ether_hdr_len = ETHER_HDR_LEN + VLAN_TAG_SIZE + 
> > + hw->vtnet_hdr_size;
> > 
> > +            uint32_t frame_size = mtu + ether_hdr_len;
> > 
> > +
> > 
> > +            if (mtu < ETHER_MIN_MTU || frame_size > 
> > + VIRTIO_MAX_RX_PKTLEN ) {
> > 
> > +                           PMD_INIT_LOG(ERR, "MTU should be between 
> > + %d and %d\n",
> > 
> > +                                         ETHER_MIN_MTU, 
> > + VIRTIO_MAX_RX_PKTLEN);
> > 
> > +                           return -EINVAL;
> > 
> > +            }
> > 
> > +            return 0;
> > 
> > +}
> > 
> > 
> > 
> > /*
> > 
> >   * dev_ops for virtio, bare necessities for basic operation
> > 
> >   */
> > 
> > @@ -677,7 +685,6 @@ static const struct eth_dev_ops virtio_eth_dev_ops 
> > = {
> > 
> >              .allmulticast_enable     = virtio_dev_allmulticast_enable,
> > 
> >              .allmulticast_disable    = virtio_dev_allmulticast_disable,
> > 
> > +            .mtu_set                 = virtio_mtu_set,
> > 
> >              .dev_infos_get           = virtio_dev_info_get,
> > 
> >              .stats_get               = virtio_dev_stats_get,
> > 
> >              .xstats_get              = virtio_dev_xstats_get,
> > 
> > --
> > 
> > Please do let me know if this looks good to you all. Thanks
> > 
> > 
> > 
> > --
> > 
> > Regards,
> > 
> > Souvik
> > 
> > 
> > 
> > -----Original Message-----
> > From: Kavanagh, Mark B [mailto:mark.b.kavanagh at intel.com]
> > Sent: Friday, September 23, 2016 5:08 AM
> > To: Yuanhan Liu <yuanhan.liu at linux.intel.com>; Stephen Hemminger 
> > <stephen at networkplumber.org>
> > Cc: Dey, Souvik <sodey at sonusnet.com>; dev at dpdk.org
> > Subject: RE: [PATCH v6] net/virtio: add set_mtu in virtio
> > 
> > 
> > 
> > >Subject: Re: [PATCH v6] net/virtio: add set_mtu in virtio
> > 
> > >
> > 
> > >On Wed, Sep 21, 2016 at 06:45:05PM -0700, Stephen Hemminger wrote:
> > 
> > >> On Thu, 22 Sep 2016 00:08:38 +0000
> > 
> > >> "Dey, Souvik" <sodey at sonusnet.com<mailto:sodey at sonusnet.com>> wrote:
> > 
> > >>
> > 
> > >> > Answers inline.
> > 
> > >> >
> > 
> > >> > --
> > 
> > >> > Regards,
> > 
> > >> > Souvik
> > 
> > >> >
> > 
> > >> > -----Original Message-----
> > 
> > >> > From: Stephen Hemminger [mailto:stephen at networkplumber.org]
> > 
> > >> > Sent: Wednesday, September 21, 2016 7:22 PM
> > 
> > >> > To: Dey, Souvik <sodey at sonusnet.com<mailto:sodey at sonusnet.com>>
> > 
> > >> > Cc: mark.b.kavanagh at intel.com<mailto:mark.b.kavanagh at intel.com>; 
> > >> > yuanhan.liu at linux.intel.com<mailto:yuanhan.liu at linux.intel.com>;
> > 
> > >> > dev at dpdk.org<mailto:dev at dpdk.org>
> > 
> > >> > Subject: Re: [PATCH v6] net/virtio: add set_mtu in virtio
> > 
> > >> >
> > 
> > >> > On Wed, 21 Sep 2016 19:11:47 -0400
> > 
> > >> > Dey <sodey at sonusnet.com<mailto:sodey at sonusnet.com>> wrote:
> > 
> > >> >
> > 
> > >> > >
> > 
> > >> > > +
> > 
> > >> > > +#define VLAN_TAG_SIZE           4    /* 802.3ac tag (not DMA'd) */
> > 
> > >> > > +
> > 
> > >> > > +static int virtio_mtu_set(struct rte_eth_dev *dev, uint16_t 
> > >> > > +mtu) {
> > 
> > >> > > +       struct rte_eth_dev_info dev_info;
> > 
> > >> > > +       uint32_t ether_hdr_len = ETHER_HDR_LEN + ETHER_CRC_LEN 
> > >> > > + + VLAN_TAG_SIZE;
> > 
> > >> > > +       uint32_t frame_size = mtu + ether_hdr_len;
> > 
> > >> > > +
> > 
> > >> > > +       virtio_dev_info_get(dev, &dev_info);
> > 
> > >> > > +
> > 
> > >> > > +       if (mtu < ETHER_MIN_MTU || frame_size > 
> > >> > > + dev_info.max_rx_pktlen) {
> > 
> > >> > > +               PMD_INIT_LOG(ERR, "MTU should be between %d and 
> > >> > > + %d\n",
> > 
> > >> > > +                               ETHER_MIN_MTU,
> > 
> > >> > > +                               (dev_info.max_rx_pktlen - 
> > >> > > + ether_hdr_len));
> > 
> > >> > > +               return -EINVAL;
> > 
> > >> > > +       }
> > 
> > >> > > +       return 0;
> > 
> > >> > > +}
> > 
> > >> >
> > 
> > >> > I am fine with the general idea of this patch but:
> > 
> > >> >   1. Calling virtio_dev_info_get is needlessly wasteful when all 
> > >> > you want
> > 
> > >> >      is to access the max packet length. Since max_rx_pktlen is 
> > >> > always
> > 
> > >> >      VIRTIO_MAX_RX_PKTLEN, please just use that.
> > 
> > >> > [Dey, Souvik] I am using the virtio_dev_info_get as in future
> > 
> > >> > can/may support the
> > 
> > >max_rx_pktlen as a variable to be set by  the application. This will
> > 
> > >keep the changes future proof. As we need to support till 65535 instead of 9728 as the linux does.
> > 
> > >>
> > 
> > >> Fine, then just dereference hw->rx_max_pktlen. Driver code 
> > >> can/should
> > 
> > >> reference its own data directly.
> > 
> > >
> > 
> > >Dey, maybe you could just use VIRTIO_MAX_RX_PKTLEN here, like what 
> > >you
> > 
> > >did in early versions.
> > 
> > >
> > 
> > >> >
> > 
> > >> >   2. Defining VLAN_TAG_SIZE is irrelevant if doing vlan offload.
> > 
> > >> > [Dey, Souvik] vlan offload is not mandatory. Se again still have
> > 
> > >> > vlan being sent up to
> > 
> > >the application. In that case we need to consider the vlan length in the Ethernet size.
> > 
> > >>
> > 
> > >> The code needs to handle both vlan offload (or not), correctly. You
> > 
> > >> are assuming the worst case here.
> > 
> > >
> > 
> > >I think we are fine here to assume worst case.
> > 
> > >
> > 
> > >> >
> > 
> > >> >   3. Virtio doesn't insert CRC, therefore CRC_LEN is irrelevant
> > 
> > >> > [Dey, Souvik] I am not sure of this. Mark commented earlier to consider this length too.
> > 
> > >Mark what do you suggest ?
> > 
> > >>
> > 
> > >> Actually, the thing that matters is the size of the merge rx buf header, not the CRC.
> > 
> 
> This patch is good enough for now, but not fully correct.
> The actual max value depends on the host negotiation protocol, ie merge rx buf is only sometimes used.
> 
> There was some discussion on netdev mailing list to pass MTU from host to guest in virtio, not sure where that landed.


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