path: root/Documentation/networking/filter.txt
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authorAlexei Starovoitov <ast@plumgrid.com>2014-03-28 18:58:25 +0100
committerDavid S. Miller <davem@davemloft.net>2014-03-31 00:45:09 -0400
commitbd4cf0ed331a275e9bf5a49e6d0fd55dffc551b8 (patch)
tree6ffb15296ce4cdc1f272e31bd43a5804b8da588c /Documentation/networking/filter.txt
parentnet: isdn: use sk_unattached_filter api (diff)
net: filter: rework/optimize internal BPF interpreter's instruction set
This patch replaces/reworks the kernel-internal BPF interpreter with an optimized BPF instruction set format that is modelled closer to mimic native instruction sets and is designed to be JITed with one to one mapping. Thus, the new interpreter is noticeably faster than the current implementation of sk_run_filter(); mainly for two reasons: 1. Fall-through jumps: BPF jump instructions are forced to go either 'true' or 'false' branch which causes branch-miss penalty. The new BPF jump instructions have only one branch and fall-through otherwise, which fits the CPU branch predictor logic better. `perf stat` shows drastic difference for branch-misses between the old and new code. 2. Jump-threaded implementation of interpreter vs switch statement: Instead of single table-jump at the top of 'switch' statement, gcc will now generate multiple table-jump instructions, which helps CPU branch predictor logic. Note that the verification of filters is still being done through sk_chk_filter() in classical BPF format, so filters from user- or kernel space are verified in the same way as we do now, and same restrictions/constraints hold as well. We reuse current BPF JIT compilers in a way that this upgrade would even be fine as is, but nevertheless allows for a successive upgrade of BPF JIT compilers to the new format. The internal instruction set migration is being done after the probing for JIT compilation, so in case JIT compilers are able to create a native opcode image, we're going to use that, and in all other cases we're doing a follow-up migration of the BPF program's instruction set, so that it can be transparently run in the new interpreter. In short, the *internal* format extends BPF in the following way (more details can be taken from the appended documentation): - Number of registers increase from 2 to 10 - Register width increases from 32-bit to 64-bit - Conditional jt/jf targets replaced with jt/fall-through - Adds signed > and >= insns - 16 4-byte stack slots for register spill-fill replaced with up to 512 bytes of multi-use stack space - Introduction of bpf_call insn and register passing convention for zero overhead calls from/to other kernel functions - Adds arithmetic right shift and endianness conversion insns - Adds atomic_add insn - Old tax/txa insns are replaced with 'mov dst,src' insn Performance of two BPF filters generated by libpcap resp. bpf_asm was measured on x86_64, i386 and arm32 (other libpcap programs have similar performance differences): 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 Raw performance data from BPF micro-benchmark: SK_RUN_FILTER on the same SKB (cache-hit) or 10k SKBs (cache-miss); time in ns 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 new BPF 31 71 47 97 old BPF jit 12 34 17 44 new 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 new 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 new BPF 180 270 330 470 old BPF jit 26 182 37 202 new BPF jit TBD Thus, without changing any userland BPF filters, applications on top of AF_PACKET (or other families) such as libpcap/tcpdump, cls_bpf classifier, netfilter's xt_bpf, team driver's load-balancing mode, and many more will have better interpreter filtering performance. While we are replacing the internal BPF interpreter, we also need to convert seccomp BPF in the same step to make use of the new internal structure since it makes use of lower-level API details without being further decoupled through higher-level calls like sk_unattached_filter_{create,destroy}(), for example. Just as for normal socket filtering, also seccomp BPF experiences a time-to-verdict speedup: 05-sim-long_jumps.c of libseccomp was used as micro-benchmark: seccomp_rule_add_exact(ctx,... seccomp_rule_add_exact(ctx,... rc = seccomp_load(ctx); for (i = 0; i < 10000000; i++) syscall(199, 100); 'short filter' has 2 rules 'large filter' has 200 rules 'short filter' performance is slightly better on x86_64/i386/arm32 'large filter' is much faster on x86_64 and i386 and shows no difference on arm32 --x86_64-- short filter old BPF: 2.7 sec 39.12% bench libc-2.15.so [.] syscall 8.10% bench [kernel.kallsyms] [k] sk_run_filter 6.31% bench [kernel.kallsyms] [k] system_call 5.59% bench [kernel.kallsyms] [k] trace_hardirqs_on_caller 4.37% bench [kernel.kallsyms] [k] trace_hardirqs_off_caller 3.70% bench [kernel.kallsyms] [k] __secure_computing 3.67% bench [kernel.kallsyms] [k] lock_is_held 3.03% bench [kernel.kallsyms] [k] seccomp_bpf_load new BPF: 2.58 sec 42.05% bench libc-2.15.so [.] syscall 6.91% bench [kernel.kallsyms] [k] system_call 6.25% bench [kernel.kallsyms] [k] trace_hardirqs_on_caller 6.07% bench [kernel.kallsyms] [k] __secure_computing 5.08% bench [kernel.kallsyms] [k] sk_run_filter_int_seccomp --arm32-- short filter old BPF: 4.0 sec 39.92% bench [kernel.kallsyms] [k] vector_swi 16.60% bench [kernel.kallsyms] [k] sk_run_filter 14.66% bench libc-2.17.so [.] syscall 5.42% bench [kernel.kallsyms] [k] seccomp_bpf_load 5.10% bench [kernel.kallsyms] [k] __secure_computing new BPF: 3.7 sec 35.93% bench [kernel.kallsyms] [k] vector_swi 21.89% bench libc-2.17.so [.] syscall 13.45% bench [kernel.kallsyms] [k] sk_run_filter_int_seccomp 6.25% bench [kernel.kallsyms] [k] __secure_computing 3.96% bench [kernel.kallsyms] [k] syscall_trace_exit --x86_64-- large filter old BPF: 8.6 seconds 73.38% bench [kernel.kallsyms] [k] sk_run_filter 10.70% bench libc-2.15.so [.] syscall 5.09% bench [kernel.kallsyms] [k] seccomp_bpf_load 1.97% bench [kernel.kallsyms] [k] system_call new BPF: 5.7 seconds 66.20% bench [kernel.kallsyms] [k] sk_run_filter_int_seccomp 16.75% bench libc-2.15.so [.] syscall 3.31% bench [kernel.kallsyms] [k] system_call 2.88% bench [kernel.kallsyms] [k] __secure_computing --i386-- large filter old BPF: 5.4 sec new BPF: 3.8 sec --arm32-- large filter old BPF: 13.5 sec 73.88% bench [kernel.kallsyms] [k] sk_run_filter 10.29% bench [kernel.kallsyms] [k] vector_swi 6.46% bench libc-2.17.so [.] syscall 2.94% bench [kernel.kallsyms] [k] seccomp_bpf_load 1.19% bench [kernel.kallsyms] [k] __secure_computing 0.87% bench [kernel.kallsyms] [k] sys_getuid new BPF: 13.5 sec 76.08% bench [kernel.kallsyms] [k] sk_run_filter_int_seccomp 10.98% bench [kernel.kallsyms] [k] vector_swi 5.87% bench libc-2.17.so [.] syscall 1.77% bench [kernel.kallsyms] [k] __secure_computing 0.93% bench [kernel.kallsyms] [k] sys_getuid BPF filters generated by seccomp are very branchy, so the new internal BPF performance is better than the old one. Performance gains will be even higher when BPF JIT is committed for the new structure, which is planned in future work (as successive JIT migrations). BPF has also been stress-tested with trinity's BPF fuzzer. Joint work with Daniel Borkmann. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Cc: Hagen Paul Pfeifer <hagen@jauu.net> Cc: Kees Cook <keescook@chromium.org> Cc: Paul Moore <pmoore@redhat.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: H. Peter Anvin <hpa@linux.intel.com> Cc: linux-kernel@vger.kernel.org Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation/networking/filter.txt')
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