Re: [net-next PATCH 0/7] tc offload for cls_u32 on ixgbe

On 16-02-09 06:24 AM, Fastabend, John R wrote:

On 2/4/2016 5:12 AM, Jamal Hadi Salim wrote:

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On 16-02-03 01:48 PM, Fastabend, John R wrote:

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Basically most hardware (or i should say driver implementations of
mostly TCAMS) allow you to add exactly the same filter as many times
as you want. They dont really look at what you want to filter on
and then scream "conflict". IOW, you (user) are responsible for
conflict resolution at the filter level. The driver sees this blob
and requests for some index/key from the hardware then just adds it.
You can then use this key/index to delete/replace etc.
This is what i meant by "append" mode.
However if a classifier implementation cares about filter ambiguity
resolution, then priorities are used. We need to worry about the
bigger picture.

Sure in other classifiers its used but its not needed in the set I
planned to added it later.

If you leave it open for some other hardware to use we should be fine.

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For this series using cls_u32 the handle gives you everything you need
to put entries in the right table and row. Namely the ht # and order #
from 'tc'.

True - but with a caveat. There are only 2^12 max tables you can
have for example and up to 2^12 filters per bucket etc.

This is a software limitation as well right? If it hasn't showed up
as a limitation on the software side why would it be an issue here?
Do you have more than 2^12 tables on your devices? If so I guess we
can tack on another 32bits somewhere.

That handle is used as an "Address" to the 32 bit filter.
Just beware of the semantics the handle has.
It hasnt shown up as a software limitation because the defaults
are good enough for most people. But if you ever want to install
a million rules that can be looked up at a reasonable pps rate
it will become very obvious quickly. I have a sample setup in the
talk tommorow which shows such an example.

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I think you need to take the u32 address and map it to something in your
hardware. But at the same time it is important to have the abstraction
closely emulate your hardware.

IMO the hardware/interface must preserve the same ordering of
filters/hash_Tables/etc. How it does that mapping should be
a driver concern and it can always abort if it fails.

Sure.

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Also ran a few tests and can't see how priority works in u32 maybe you
can shed some light but as best I can tell it doesn't have any effect
on rule execution.

True.
u32 doesnt care because it will give you a nodeid if you dont specify
one. i.e conflict resolution is mapped to you not specifying exactly
the same ht:bkt:nodeid more than once. And if you will let the
kernel do it for you (as i am assumming you are saying your hardware
will) then no need.

Yep. Faithfully offloading u32 here not changing anything except
I do have to abort on some cases with the simpler devices. fm10k for
example can model hash nodes with divisors > 1.

I wonder if when we get to capabilities we can do this...

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My issue is we can map flower onto u32 that is fine and u32 onto
bpf. But we lose a lot of the power of each classifier when we
do this. flower for example is nice because of its simplicity
presumably this translates into faster updates, u32 is great because
we get full parse graph support and hash tables, ebpf is the biggest
beast of all and lets us load arbitrary functions into the device.
All are nice in their own right.

Did i send you my slides? ;->


cheers,
jamal