On Fri, Jun 19, 2020 at 3:21 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > 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'm totally fine waiting for John's tests, but I read your reply as a request to go dig up some more examples from sysdig and other projects, which I don't think I can commit to. So if it's just about waiting for John's examples, that's fine and sorry for misunderstanding. > > > 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: Yep, sorry, I assumed more general context, not specifically John's reply. > > >>> 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
