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Date: Fri, 23 Sep 2016 15:53:20 +0800
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: "Dey, Souvik" <sodey@sonusnet.com>,
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Subject: Re: [dpdk-dev] [PATCH v6] net/virtio: add set_mtu in virtio
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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@sonusnet.com> wrote:
>
> > Answers inline.
> >
> > --
> > Regards,
> > Souvik
> >
> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > Sent: Wednesday, September 21, 2016 7:22 PM
> > To: Dey, Souvik <sodey@sonusnet.com>
> > Cc: mark.b.kavanagh@intel.com; yuanhan.liu@linux.intel.com; dev@dpdk.org
> > Subject: Re: [PATCH v6] net/virtio: add set_mtu in virtio
> >
> > On Wed, 21 Sep 2016 19:11:47 -0400
> > Dey <sodey@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.
Right.
--yliu
>
> The patch is still buggy.
>