On Mon, Oct 07, 2013 at 06:53:43PM +0200, Hannes Frederic Sowa wrote:

Hi Jon!

Maybe I got the wrong email address for the neterion driver from the
maintainers filer? If you are (still) affiliated with the neterion driver,
maybe you could have a short look at the quoted mail below?

Both are valid email addresses, but I prefer to address non-Intel
issues with my kudzu.us email account.

I apologize for not addressing your question yet.  What you are saying
makes sense, but I want to dig through the documentation and verify.
However, I haven't had the time.  I'll brew up a pot of coffee when I
get home and I'll get an answer to you before I go to bed tonight :)

Thanks,
Jon

Thanks,

  Hannes

On Wed, Oct 02, 2013 at 06:27:30PM +0200, Hannes Frederic Sowa wrote:

quoted

Hi!

I have a question regarding UFO and the neterion driver, which as the only one
advertises hardware UFO support:

The patch discusses in this thread
http://thread.gmane.org/gmane.linux.network/284348/focus=285405 could change
some semantics how packets are constructed before submitted to the driver.

We currently guarantee that we have the MAC/IP/UDP header in skb->data and the
payload is attached in the skb's frags. With the changes discussed in this
thread it is possible that we also append to skb->data some amount of data
which is not targeted for the header. From reading the driver sources it seems
the hardware interprets the skb->data to skb_headlen as the header, so we
could include some data in the fragments more than once.

Do you think this change is safe? Otherwise I would suggest that the UFO
capability is switched off until the driver signals the hardware the start and
end of the headers correctly?

I left the mail below intact which points to the specific place in s2io.c
where I think the problem is.

On Wed, Oct 02, 2013 at 08:14:27AM -0700, Eric Dumazet wrote:

quoted

On Wed, 2013-10-02 at 15:03 +0200, Hannes Frederic Sowa wrote:

quoted

On Wed, Oct 02, 2013 at 02:12:07PM +0200, Hannes Frederic Sowa wrote:

quoted

Hi Eric!

On Wed, Oct 02, 2013 at 03:41:28AM -0700, Eric Dumazet wrote:

quoted

On Wed, 2013-10-02 at 10:58 +0200, Jiri Pirko wrote:

quoted

Wed, Oct 02, 2013 at 01:25:34AM CEST, hannes@stressinduktion.org wrote:

quoted

-	if (((length > mtu) || (skb && skb_is_gso(skb))) &&
+	if (((length > mtu) || (skb && skb_has_frags(skb))) &&

quoted

This seems correct to me. sk_is_gso would work as well is you apply my
patch "[patch net] ip6_output: do skb ufo init for peeked non ufo skb as
well" which does the setting of gso_size.

Well, skb having frags or not should not be a concern :
Thats an allocation choice (lets say to avoid high order allocations). 

Setting gso_size is probably better.

e89e9cf539a28df7d0eb1d0a545368e9920b34ac ("[IPv4/IPv6]: UFO Scatter-gather
approach") states:

"
skb->data will contain MAC/IP/UDP header and skb_shinfo(skb)->frags[]
contains the data payload. The skb->ip_summed will be set to CHECKSUM_HW
indicating that hardware has to do checksum calculation. Hardware should
compute the UDP checksum of complete datagram and also ip header checksum of
each fragmented IP packet.
"

This is the reason why I tried not to update the gso_size. If it is ok, I am
fine with that.

Especially, drivers/net/ethernet/neterion/s2io.c states that the first dma
mapping (skb->data with skb_headlen, which is fine) is used as the inband
header:

        if (offload_type == SKB_GSO_UDP)
                frg_cnt++; /* as Txd0 was used for inband header */

That is my only other hint that we maybe should not update gso_size and
gso_type. I guess software fallback does not have this problem, but I won't
have time to check until this evening.

I am really not sure if just setting gso_size does not break neterion UFO
offloading. :/

Well, just ask Jon Mason to double check ;)

I think the commit intent was to set gso_size :

   skb_shinfo(skb)->ufo_size will indicate the length of data part in each IP
    fragment going out of the adapter after IP fragmentation by hardware.

The fact that it states "skb->data will contain MAC/IP/UDP header and
skb_shinfo(skb)->frags[] contains the data payload." seems irrelevant.

If Neterion driver mandates that skb->head *only* contains the
MAC/IP/UDP header, that should be handled in the driver itself.

Thanks Eric for clearing this up.

I really thought it would be the common pattern for UFO to have only headers
in skb->data, so I didn't bother to ask in the first place.

Thanks,

  Hannes

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