On 6/19/20 8:41 PM, Andrii Nakryiko wrote:
On Fri, Jun 19, 2020 at 6:08 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
On 6/19/20 2:39 AM, John Fastabend wrote:
John Fastabend wrote:
Andrii Nakryiko wrote:
On Thu, Jun 18, 2020 at 11:58 AM John Fastabend
<john.fastabend@xxxxxxxxx> wrote:
[...]
That would be great. Self-tests do work, but having more testing with
real-world application would certainly help as well.
Thanks for all the follow up.
I ran the change through some CI on my side and it passed so I can
complain about a few shifts here and there or just update my code or
just not change the return types on my side but I'm convinced its OK
in most cases and helps in some so...
Acked-by: John Fastabend <john.fastabend@xxxxxxxxx>
I'll follow this up with a few more selftests to capture a couple of our
patterns. These changes are subtle and I worry a bit that additional
<<,s>> pattern could have the potential to break something.
Another one we didn't discuss that I found in our code base is feeding
the output of a probe_* helper back into the size field (after some
alu ops) of subsequent probe_* call. Unfortunately, the tests I ran
today didn't cover that case.
I'll put it on the list tomorrow and encode these in selftests. I'll
let the mainainers decide if they want to wait for those or not.
Given potential fragility on verifier side, my preference would be that we
have the known variations all covered in selftests before moving forward in
order to make sure they don't break in any way. Back in [0] I've seen mostly
similar cases in the way John mentioned in other projects, iirc, sysdig was
another one. If both of you could hack up the remaining cases we need to
cover and then submit a combined series, that would be great. I don't think
we need to rush this optimization w/o necessary selftests.
There is no rush, but there is also no reason to delay it. I'd rather
land it early in the libbpf release cycle and let people try it in
their prod environments, for those concerned about such code patterns.
Andrii, define 'delay'. John mentioned above to put together few more
selftests today so that there is better coverage at least, why is that
an 'issue'? I'm not sure how you read 'late in release cycle' out of it,
it's still as early. The unsigned optimization for len <= MAX_LEN is
reasonable and makes sense, but it's still one [specific] variant only.
I don't have a list of all the patterns that we might need to test.
Going through all open-source BPF source code to identify possible
patterns and then coding them up in minimal selftests is a bit too
much for me, honestly.
I think we're probably talking past each other. John wrote above:
>>> I'll follow this up with a few more selftests to capture a couple of our
>>> patterns. These changes are subtle and I worry a bit that additional
>>> <<,s>> pattern could have the potential to break something.
So submitting this as a full series together makes absolutely sense to me,
so there's maybe not perfect but certainly more confidence that also other
patterns where the shifts optimized out in one case are then appearing in
another are tested on a best effort and run our kselftest suite.
Thanks,
Daniel
