Re: [PATCH v7 net-next 1/3] filter: add Extended BPF interpreter and converter

[Eric Dumazet]

On Sun, 2014-03-09 at 10:38 -0700, Alexei Starovoitov wrote:
> On Sun, Mar 9, 2014 at 7:45 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> > On Sat, 2014-03-08 at 15:15 -0800, Alexei Starovoitov wrote:
> >
> >> +/**
> >> + *   sk_run_filter_ext - run an extended filter
> >> + *   @ctx: buffer to run the filter on
> >> + *   @insn: filter to apply
> >> + *
> >> + * Decode and execute extended BPF instructions.
> >> + * @ctx is the data we are operating on.
> >> + * @filter is the array of filter instructions.
> >> + */
> >> +notrace u32 sk_run_filter_ext(void *ctx, const struct sock_filter_ext *insn)
> >> +{
> >> +     u64 stack[64];
> >> +     u64 regs[16];
> >> +     void *ptr;
> >> +     u64 tmp;
> >> +     int off;
> 
> First of all, great that you finally reviewed it! Feedback is appreciated :)
> 
> > Why is this 'notrace' ?
> 
> to avoid overhead of dummy call.
> JITed filters are not adding this dummy call.
> So 'notrace' on interpreter brings it to parity with JITed filters.

Then its a wrong reason.

At the time we wrote JIT, there was (yet) no support for profiling JIT
from perf tools. I asked for help and nobody answered.

Maybe this has changed, if so, please someone add support.


> 
> > 80 u64 on the stack, that is 640 bytes to run a filter ????
> 
> yes. that was described in commit log and in Doc...filter.txt:
> "
> - 16 4-byte stack slots for register spill-fill replaced with
>   up to 512 bytes of multi-use stack space
> "
> 
> For interpreter it is prohibitive to dynamically allocate stack space
> that's why it just grabs 64*8 to run any program.

Where is checked the max capacity of this stack ?



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