On 29.10.2012 22:40, YongHyeon PYUN wrote:
On Mon, Oct 29, 2012 at 09:21:00AM +0400, Gleb Smirnoff wrote:
On Mon, Oct 29, 2012 at 01:41:04PM -0700, YongHyeon PYUN wrote:
Y> On Sun, Oct 28, 2012 at 02:01:37AM +0400, Gleb Smirnoff wrote:
Y> > On Sat, Oct 27, 2012 at 12:58:52PM +0200, Andre Oppermann wrote:
Y> > A> On 26.10.2012 23:06, Gleb Smirnoff wrote:
Y> > A> > Author: glebius
Y> > A> > Date: Fri Oct 26 21:06:33 2012
Y> > A> > New Revision: 242161
Y> > A> > URL: http://svn.freebsd.org/changeset/base/242161
Y> > A> >
Y> > A> > Log:
Y> > A> > o Remove last argument to ip_fragment(), and obtain all needed
information
Y> > A> > on checksums directly from mbuf flags. This simplifies code.
Y> > A> > o Clear CSUM_IP from the mbuf in ip_fragment() if we did checksums
in
Y>
Y> I'm not sure whether ti(4)'s checksum offloading for IP fragmented
Y> packets(CSUM_IP_FRAGS) still works after this change. ti(4)
Y> requires CSUM_IP should be set for IP fragmented packets. Not sure
Y> whether it's a bug or not. I have a ti(4) controller but I don't
Y> remember where I can find it and don't have a link
Y> parter(1000baseSX) to test it. :-(
ti(4) declares both CSUM_IP and CSUM_IP_FRAGS, so ip_fragment() won't do
Because it supports both CSUM_IP and CSUM_IP_FRAGS. Probably ti(4)
is the only controller that supports TCP/UDP checksum offloading
for an IP fragmented packet.
This is a bit weird if it doesn't do the fragmentation itself.
Computing the IP header checksum doesn't differ for normal and
fragmented packets. The protocol checksum (TCP or UDP) stays
the same for in the case of IP level fragmentation. It is only
visible in the first fragment which includes the protocol header.
software checksums, and thus won't clear these flags.
Potentially a driver that announces one flag in if_hwassist but relies on
couple of flags to be set on mbuf is not correct. If a driver can't do single
checksum processing independently from others, then it should set or clear
appropriate flags in if_hwassist as a group.
Hmm, then what would be best way to achieve CSUM_IP_FRAGS in
driver? I don't have clear idea how to utilize the hardware
feature. The stack should tell that the mbuf needs TCP/UDP checksum
offloading for IP fragmented packet(i.e. CSUM_IP_FRAGS is not set by
upper stack).
As I said there can't be fragment checksumming without hardware
based fragmentation. We have three cases here:
1. TSO where the hardware does the segmentation, TCP and IP header
checksums for each generated packet.
2. IP packet fragmentation where a packet is split, the IP header
checksum is recomputed for each fragment, but the protocol csum
stays the same and is not modified.
3. UDP fragmentation where a large packet is sent to the hardware
and it generates first the UDP checksum and then splits it into
IP fragments each with its own IP header checksum.
So we end up with these possible large send hardware offload capabilities:
TSO: including IPv4hdr and TCP checksumming
UDP fragmentation: including IPv4hdr and UDP checksumming
IP fragmentation: including IPv4hdr checksumming
Besides that we have the packet <= MTU sized offload capabilities:
TCP checksumming
UDP checksumming
SCTP checksumming
IPv4hdr checksumming
Y> > A> > hardware. Some driver may not announce CSUM_IP in theur
if_hwassist,
^^^^^^^^
Oh, that was a typo! Software was meant.
That explains quite a bit of confusion.
--
Andre
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