On 12/5/23 5:23 PM, Jamal Hadi Salim wrote:
On Tue, Dec 5, 2023 at 8:43 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
On 12/5/23 1:32 AM, John Fastabend wrote:
Jamal Hadi Salim wrote:
Introduce P4 tc classifier. A tc filter instantiated on this classifier
is used to bind a P4 pipeline to one or more netdev ports. To use P4
classifier you must specify a pipeline name that will be associated to
this filter, a s/w parser and datapath ebpf program. The pipeline must have
already been created via a template.
For example, if we were to add a filter to ingress of network interface
device $P0 and associate it to P4 pipeline simple_l3 we'd issue the
following command:
In addition to my comments from last iteration.
tc filter add dev $P0 parent ffff: protocol all prio 6 p4 pname simple_l3 \
action bpf obj $PARSER.o section prog/tc-parser \
action bpf obj $PROGNAME.o section prog/tc-ingress
Having multiple object files is a mistake IMO and will cost
performance. Have a single object file avoid stitching together
metadata and run to completion. And then run entirely from XDP
this is how we have been getting good performance numbers.
+1, fully agree.
As I stated earlier: while performance is important it is not the
highest priority for what we are doing, rather correctness is. We dont
want to be wrestling with the verifier or some other limitation like
tail call limits to gain some increase in a few kkps. We are taking a
gamble with the parser which is not using any kfuncs at the moment.
Putting them all in one program will increase the risk.
I don't think this is a good reason, this corners you into UAPI which
later on cannot be changed anymore. If you encounter such issues, then
why not bringing up actual concrete examples / limitations you run into
to the BPF community and help one way or another to get the verifier
improved instead? (Again, see sched_ext as one example improving verifier,
but also concrete example bug reports, etc could help.)
As i responded to you earlier, we just dont want to lose
functionality, some sample space:
- we could have multiple pipelines with different priorities - and
each pipeline may have its own logic with many tables etc (and the
choice to iterate the next one is essentially encoded in the tc action
codes)
- we want to be able to split the pipeline into parts that can run _in
unison_ in h/w, xdp, and tc
So parser at XDP, but then you push it up the stack (instead of staying
only at XDP layer) just to reach into tc layer to perform a corresponding
action.. and this just to work around verifier as you say?
- we use tc block to map groups of ports heavily
- we use netlink as our control API
$PROGNAME.o and $PARSER.o is a compilation of the eBPF programs generated
by the P4 compiler and will be the representation of the P4 program.
Note that filter understands that $PARSER.o is a parser to be loaded
at the tc level. The datapath program is merely an eBPF action.
Note we do support a distinct way of loading the parser as opposed to
making it be an action, the above example would be:
tc filter add dev $P0 parent ffff: protocol all prio 6 p4 pname simple_l3 \
prog type tc obj $PARSER.o ... \
action bpf obj $PROGNAME.o section prog/tc-ingress
We support two types of loadings of these initial programs in the pipeline
and differentiate between what gets loaded at tc vs xdp by using syntax of
either "prog type tc obj" or "prog type xdp obj"
For XDP:
tc filter add dev $P0 ingress protocol all prio 1 p4 pname simple_l3 \
prog type xdp obj $PARSER.o section parser/xdp \
pinned_link /sys/fs/bpf/mylink \
action bpf obj $PROGNAME.o section prog/tc-ingress
I don't think tc should be loading xdp programs. XDP is not 'tc'.
For XDP, we do have a separate attach API, for BPF links we have bpf_xdp_link_attach()
via bpf(2) and regular progs we have the classic way via dev_change_xdp_fd() with
IFLA_XDP_* attributes. Mid-term we'll also add bpf_mprog support for XDP to allow
multi-user attachment. tc kernel code should not add yet another way of attaching XDP,
this should just reuse existing uapi infra instead from userspace control plane side.
I am probably missing something. We are not loading the XDP program -
it is preloaded, the only thing the filter does above is grabbing a
reference to it. The P4 pipeline in this case is split into a piece
(the parser) that runs on XDP and some that runs on tc. And as i
mentioned earlier we could go further another piece which is part of
the pipeline may run in hw. And infact in the future a compiler will
be able to generate code that is split across machines. For our s/w
datapath on the same node the only split is between tc and XDP.
So it is even worse from a design PoV. The kernel side allows XDP program
to be passed to cls_p4, but then it's not doing anything but holding a
reference to that BPF program. Iow, you need anyway to go the regular way
of bpf_xdp_link_attach() or dev_change_xdp_fd() to install XDP. Why is the
reference even needed here, why it cannot be done in user space from your
control plane? This again, feels like a shim layer which should live in
user space instead.
The theory of operations is as follows:
================================1. PARSING================================
The packet first encounters the parser.
The parser is implemented in ebpf residing either at the TC or XDP
level. The parsed header values are stored in a shared eBPF map.
When the parser runs at XDP level, we load it into XDP using tc filter
command and pin it to a file.
=============================2. ACTIONS=============================
In the above example, the P4 program (minus the parser) is encoded in an
action($PROGNAME.o). It should be noted that classical tc actions
continue to work:
IOW, someone could decide to add a mirred action to mirror all packets
after or before the ebpf action.
tc filter add dev $P0 parent ffff: protocol all prio 6 p4 pname simple_l3 \
prog type tc obj $PARSER.o section parser/tc-ingress \
action bpf obj $PROGNAME.o section prog/tc-ingress \
action mirred egress mirror index 1 dev $P1 \
action bpf obj $ANOTHERPROG.o section mysect/section-1
It should also be noted that it is feasible to split some of the ingress
datapath into XDP first and more into TC later (as was shown above for
example where the parser runs at XDP level). YMMV.
Is there any performance value in partial XDP and partial TC? The main
wins we see in XDP are when we can drop, redirect, etc the packet
entirely in XDP and avoid skb altogether.
Co-developed-by: Victor Nogueira <victor@xxxxxxxxxxxx>
Signed-off-by: Victor Nogueira <victor@xxxxxxxxxxxx>
Co-developed-by: Pedro Tammela <pctammela@xxxxxxxxxxxx>
Signed-off-by: Pedro Tammela <pctammela@xxxxxxxxxxxx>
Signed-off-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
The cls_p4 is roughly a copy of {cls,act}_bpf, and from a BPF community side
we moved away from this some time ago for the benefit of a better management
API for tc BPF programs via bpf(2) through bpf_mprog (see libbpf and BPF selftests
around this), as mentioned earlier. Please use this instead for your userspace
control plane, otherwise we are repeating the same mistakes from the past again
that were already fixed.
Sorry, that is your use case for kubernetes and not ours. We want to
There is nothing specific to k8s, it's generic infrastructure for tc BPF
and also used outside of k8s scope; please double-check the selftests to
get a picture of the API and libbpf integration.
use the tc infra. We want to use netlink. I could be misreading what
you are saying but it seems that you are suggesting that tc infra is
now obsolete as far as ebpf is concerned? Overall: It is a bit selfish
to say your use case dictates how other people use ebpf. ebpf is just
a means to an end for us and _is not the end goal_ - just an infra
toolset.
Not really, the infrastructure is already there and ready to be used and
it supports basic building blocks such as BPF links, relative prog/link
dependency resolution, etc, where none of it can be found here. The
problem is "we want to use netlink" which is even why you need to push
down things like XDP prog, but it's broken by design, really. You are
trying to push down a control plane into netlink which should have been
a framework in user space.
If you feel we should unify the P4 classifier with the tc ebpf
classifier etc then we are going to need some changes that are not
going to be useful for other people. And i dont see the point in that.
cheers,
jamal
Therefore, from BPF side:
Nacked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cheers,
Daniel
