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Date: Tue, 04 Mar 2014 10:59:42 +0100
From: Daniel Borkmann <dborkman@...hat.com>
To: Alexei Starovoitov <ast@...mgrid.com>
CC: "David S. Miller" <davem@...emloft.net>,
Ingo Molnar <mingo@...nel.org>, Will Drewry <wad@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
"H. Peter Anvin" <hpa@...or.com>,
Hagen Paul Pfeifer <hagen@...u.net>,
Jesse Gross <jesse@...ira.com>,
Thomas Gleixner <tglx@...utronix.de>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Tom Zanussi <tom.zanussi@...ux.intel.com>,
Jovi Zhangwei <jovi.zhangwei@...il.com>,
Eric Dumazet <edumazet@...gle.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Arnaldo Carvalho de Melo <acme@...radead.org>,
Pekka Enberg <penberg@....fi>,
Arjan van de Ven <arjan@...radead.org>,
Christoph Hellwig <hch@...radead.org>,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v4 net-next 1/3] Extended BPF interpreter and converter
On 03/04/2014 06:18 AM, 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@...mgrid.com>
Looks great, imho, some comments/questions inline:
Nit: subject line of your patches should be, e.g.
"filter: add Extended BPF interpreter and converter"
"doc: filter: add Extended BPF documentation"
...
so first "<subsystem>: <summary phrase>".
> ---
> include/linux/filter.h | 8 +-
> include/linux/netdevice.h | 1 +
> include/uapi/linux/filter.h | 34 +-
> net/core/filter.c | 802 ++++++++++++++++++++++++++++++++++++++++++-
> net/core/sysctl_net_core.c | 7 +
> 5 files changed, 830 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index e568c8ef896b..0e84ff6e991b 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -52,7 +52,13 @@ extern int sk_detach_filter(struct sock *sk);
> extern int sk_chk_filter(struct sock_filter *filter, unsigned int flen);
> extern int sk_get_filter(struct sock *sk, struct sock_filter __user *filter, unsigned len);
> extern void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to);
> +/* function remaps 'sock_filter' insns to 'sock_filter_ext' insns */
> +int sk_convert_filter(struct sock_filter *old_prog, int len,
> + struct sock_filter_ext *new_prog, int *p_new_len);
> +/* execute extended bpf program */
I think this and the above comment can be omitted, as both have a kernel doc
in its implementation in net/core/filter.c that is more precise.
...
> +struct sock_filter_ext {
> + __u8 code; /* opcode */
> + __u8 a_reg:4; /* dest register */
> + __u8 x_reg:4; /* source register */
> + __s16 off; /* signed offset */
> + __s32 imm; /* signed immediate constant */
> +};
> +
> struct sock_fprog { /* Required for SO_ATTACH_FILTER. */
> unsigned short len; /* Number of filter blocks */
> struct sock_filter __user *filter;
> @@ -45,12 +54,15 @@ struct sock_fprog { /* Required for SO_ATTACH_FILTER. */
> #define BPF_JMP 0x05
> #define BPF_RET 0x06
> #define BPF_MISC 0x07
> +#define BPF_ALU64 0x07
> +
>
Please do not add empty newline above.
> /* ld/ldx fields */
> #define BPF_SIZE(code) ((code) & 0x18)
> #define BPF_W 0x00
> #define BPF_H 0x08
> #define BPF_B 0x10
...
> diff --git a/net/core/filter.c b/net/core/filter.c
> index ad30d626a5bd..1494421486b7 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -1,5 +1,6 @@
> /*
> * Linux Socket Filter - Kernel level socket filtering
> + * Extended BPF is Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
> *
> * Author:
> * Jay Schulist <jschlst@...ba.org>
> @@ -40,6 +41,8 @@
> #include <linux/seccomp.h>
> #include <linux/if_vlan.h>
>
> +int bpf_ext_enable __read_mostly;
> +
> /* No hurry in this branch
> *
> * Exported for the bpf jit load helper.
> @@ -399,6 +402,7 @@ load_b:
> }
>
> return 0;
> +#undef K
> }
> EXPORT_SYMBOL(sk_run_filter);
...
> + /* RET_K, RET_A are remaped into 2 insns */
> + case BPF_RET | BPF_A:
> + case BPF_RET | BPF_K:
> + insn->code = BPF_ALU | BPF_MOV |
> + (BPF_SRC(fp->code) == BPF_K ? BPF_K : BPF_X);
Hmm, so the case statement is about BPF_RET | BPF_A and BPF_RET | BPF_K
but BPF_RET | BPF_X is not mentioned. However, in BPF_SRC(fp->code)
selection you fall back to BPF_X if it doesn't equal BPF_K? Is that
correct? And, you probably also need to handle BPF_RET | BPF_X ?
> + insn->a_reg = 0;
> + insn->x_reg = 6;
> + insn->imm = fp->k;
> +
> + insn++;
> + insn->code = BPF_RET | BPF_K;
> + break;
...
> + /* RET */
> +BPF_RET_BPF_K_0:
> + return regs[0/* R0 */];
--
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