Re: [PATCH v5 net-next 1/3] filter: add Extended BPF interpreter and converter

[Daniel Borkmann <dborkman@redhat.com>]

On 03/04/2014 11:17 PM, Alexei Starovoitov wrote:
> Extended BPF extends old BPF in the following ways:
> - from 2 to 10 registers
>    Original BPF has two registers (A and X) and hidden frame pointer.
>    Extended BPF has ten registers and read-only frame pointer.
> - from 32-bit registers to 64-bit registers
>    semantics of old 32-bit ALU operations are preserved via 32-bit
>    subregisters
> - if (cond) jump_true; else jump_false;
>    old BPF insns are replaced with:
>    if (cond) jump_true; /* else fallthrough */
> - adds signed > and >= insns
> - 16 4-byte stack slots for register spill-fill replaced with
>    up to 512 bytes of multi-use stack space
> - introduces bpf_call insn and register passing convention for zero
>    overhead calls from/to other kernel functions (not part of this patch)
> - adds arithmetic right shift insn
> - adds swab32/swab64 insns
> - adds atomic_add insn
> - old tax/txa insns are replaced with 'mov dst,src' insn
>
> Extended BPF is designed to be JITed with one to one mapping, which
> allows GCC/LLVM backends to generate optimized BPF code that performs
> almost as fast as natively compiled code
>
> sk_convert_filter() remaps old style insns into extended:
> 'sock_filter' instructions are remapped on the fly to
> 'sock_filter_ext' extended instructions when
> sysctl net.core.bpf_ext_enable=1
>
> Old filter comes through sk_attach_filter() or sk_unattached_filter_create()
>   if (bpf_ext_enable) {
>      convert to new
>      sk_chk_filter() - check old bpf
>      use sk_run_filter_ext() - new interpreter
>   } else {
>      sk_chk_filter() - check old bpf
>      if (bpf_jit_enable)
>          use old jit
>      else
>          use sk_run_filter() - old interpreter
>   }
>
> sk_run_filter_ext() interpreter is noticeably faster
> than sk_run_filter() for two reasons:
>
> 1.fall-through jumps
>    Old BPF jump instructions are forced to go either 'true' or 'false'
>    branch which causes branch-miss penalty.
>    Extended BPF jump instructions have one branch and fall-through,
>    which fit CPU branch predictor logic better.
>    'perf stat' shows drastic difference for branch-misses.
>
> 2.jump-threaded implementation of interpreter vs switch statement
>    Instead of single tablejump at the top of 'switch' statement, GCC will
>    generate multiple tablejump instructions, which helps CPU branch predictor
>
> Performance of two BPF filters generated by libpcap was measured
> on x86_64, i386 and arm32.
>
> fprog #1 is taken from Documentation/networking/filter.txt:
> tcpdump -i eth0 port 22 -dd
>
> fprog #2 is taken from 'man tcpdump':
> tcpdump -i eth0 'tcp port 22 and (((ip[2:2] - ((ip[0]&0xf)<<2)) -
>     ((tcp[12]&0xf0)>>2)) != 0)' -dd
>
> Other libpcap programs have similar performance differences.
>
> Raw performance data from BPF micro-benchmark:
> SK_RUN_FILTER on same SKB (cache-hit) or 10k SKBs (cache-miss)
> time in nsec per call, smaller is better
> --x86_64--
>           fprog #1  fprog #1   fprog #2  fprog #2
>           cache-hit cache-miss cache-hit cache-miss
> old BPF     90       101       192       202
> ext BPF     31        71       47         97
> old BPF jit 12        34       17         44
> ext BPF jit TBD
>
> --i386--
>           fprog #1  fprog #1   fprog #2  fprog #2
>           cache-hit cache-miss cache-hit cache-miss
> old BPF    107        136      227       252
> ext BPF     40        119       69       172
>
> --arm32--
>           fprog #1  fprog #1   fprog #2  fprog #2
>           cache-hit cache-miss cache-hit cache-miss
> old BPF    202        300      475       540
> ext BPF    139        270      296       470
> old BPF jit 26        182       37       202
> new BPF jit TBD
>
> Tested with trinify BPF fuzzer
>
> Future work:
>
> 0. seccomp
>
> 1. add extended BPF JIT for x86_64
>
> 2. add inband old/new demux and extended BPF verifier, so that new programs
>     can be loaded through old sk_attach_filter() and sk_unattached_filter_create()
>     interfaces
>
> 3. tracing filters systemtap-like with extended BPF
>
> 4. OVS with extended BPF
>
> 5. nftables with extended BPF
>
> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
> Acked-by: Hagen Paul Pfeifer <hagen@jauu.net>

 From what I can tell, looks good to me:

Reviewed-by: Daniel Borkmann <dborkman@redhat.com>

So next step would be to add selftests and then after that JIT?

...
> +#undef LOAD_IMM
> +}
> +EXPORT_SYMBOL(sk_run_filter_ext);
> +

One minor thing I noticed when I git-am'ed your patch is the newline at
the end of file, but perhaps this can be fixed up in directly patchwork.

> diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
> index cf9cd13509a7..e1b979312588 100644
> --- a/net/core/sysctl_net_core.c
> +++ b/net/core/sysctl_net_core.c