On Tue, Sep 26, 2017 at 09:47:21PM -0700, David Miller wrote:
> From: Mika Westerberg <mika.westerb...@linux.intel.com>
> Date: Mon, 25 Sep 2017 14:07:38 +0300
>
> > +struct thunderbolt_ip_header {
> > + u32 route_hi;
> > + u32 route_lo;
> > + u32 length_sn;
> > + uuid_t uuid;
> > + uuid_t initiator_uuid;
> > + uuid_t target_uuid;
> > + u32 type;
> > + u32 command_id;
> > +} __packed;
>
> Again, the __packed attribute should not be necessary and needs to be
> removed.
OK, will do.
> > +static void tbnet_pull_tail(struct sk_buff *skb)
> > +{
> > + skb_frag_t *frag = &skb_shinfo(skb)->frags[0];
> > + unsigned int pull_len;
> > + void *hdr;
> > +
> > + hdr = skb_frag_address(frag);
> > + pull_len = eth_get_headlen(hdr, TBNET_RX_HDR_SIZE);
> > +
> > + /* Align pull length to size of long to optimize memcpy performance */
> > + skb_copy_to_linear_data(skb, hdr, ALIGN(pull_len, sizeof(long)));
>
> You do not need to copy here, instead you can build SKB's where the
> skb->data points directly at the head of your first frag page memory.
>
> See build_skb().
>
> > + skb = net->skb;
> > + if (!skb) {
> > + skb = netdev_alloc_skb_ip_align(net->dev,
> > + TBNET_RX_HDR_SIZE);
> > + net->skb = skb;
> > + }
> > + if (!skb)
> > + break;
> > +
> > + /* Single small buffer we can copy directly to the
> > + * header part of the skb.
> > + */
> > + if (hdr->frame_count == 1 && frame_size <= TBNET_RX_HDR_SIZE) {
>
> Here you would use build_skb() instead of netdev_alloc_skb*() for the first
> frag, and keep the existing code tacking on subsequent frags using
> skb_add_Rx_frag().
I'm reading kernel-doc of build_skb() (or rather __build_skb()) and it
says caller needs to reserve head room of NET_SKB_PAD and then make sure
there is space for SKB_DATA_ALIGN(skb_shared_info).
Now, in case of ThunderboltIP frames, they look like this:
+---------+
| hdr | 12 bytes
+---------+
| data | 4096 - 12 = 4084 bytes
| |
| |
+---------+
A packet can consist of multiple frames where each have the 12-byte
header and 4084 bytes of TSO/LRO payload except the last one which can
be smaller than 4084.
Using build_skb() then would require to allocate larger buffer, that
includes NET_SKB_PAD + SKB_DATA_ALIGN(skb_shared_info) and that exceeds
page size. Is this something supported by build_skb()? It was not clear
to me based on the code and other users of build_skb() but I may be
missing something.
> > + ret = register_netdev(dev);
> > + if (ret) {
> > + free_netdev(dev);
> > + return ret;
> > + }
> > +
> > + net->handler.uuid = &tbnet_svc_uuid;
> > + net->handler.callback = tbnet_handle_packet,
> > + net->handler.data = net;
> > + tb_register_protocol_handler(&net->handler);
> > +
> > + tb_service_set_drvdata(svc, net);
>
> There could be races here.
>
> At the exact moment you call register_netdev(), your device can be
> brought UP, packets transmitted, etc. You entire set of driver code
> paths can be executed.
>
> The rest of those initializations after register_netdev() probably
> are needed by the rest of the driver to function properly, so may
> need to happen before register_netdev() publishes the device to the
> entire world.
You're right. I'll change the ordering so that register_netdev() happens
last.
Thanks!
