>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> 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> >> > Cc: mark.b.kavanagh at intel.com; yuanhan.liu at linux.intel.com; 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> 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.
My comments were based on my experience with DPDK ethdev PMDs - Stephen and Yuanhan have much more experience with virtio, so I'd go with their suggestion. > > --yliu >> >> The patch is still buggy. >>
