Messages in this thread | | | Date | Thu, 5 Dec 2013 11:41:13 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH tip 0/5] tracing filters with BPF |
| |
* Alexei Starovoitov <ast@plumgrid.com> wrote:
> > On Tue, Dec 3, 2013 at 4:01 PM, Andi Kleen <andi@firstfloor.org> wrote: > >> > >> Can you do some performance comparison compared to e.g. ktap? > >> How much faster is it? > > Did simple ktap test with 1M alloc_skb/kfree_skb toy test from earlier email: > trace skb:kfree_skb { > if (arg2 == 0x100) { > printf("%x %x\n", arg1, arg2) > } > } > 1M skb alloc/free 350315 (usecs) > > baseline without any tracing: > 1M skb alloc/free 145400 (usecs) > > then equivalent bpf test: > void filter(struct bpf_context *ctx) > { > void *loc = (void *)ctx->regs.dx; > if (loc == 0x100) { > struct sk_buff *skb = (struct sk_buff *)ctx->regs.si; > char fmt[] = "skb %p loc %p\n"; > bpf_trace_printk(fmt, sizeof(fmt), (long)skb, (long)loc, 0); > } > } > 1M skb alloc/free 183214 (usecs) > > so with one 'if' condition the difference ktap vs bpf is 350-145 vs 183-145 > > obviously ktap is an interpreter, so it's not really fair. > > To make it really unfair I did: > trace skb:kfree_skb { > if (arg2 == 0x100 || arg2 == 0x200 || arg2 == 0x300 || arg2 == 0x400 || > arg2 == 0x500 || arg2 == 0x600 || arg2 == 0x700 || arg2 == 0x800 || > arg2 == 0x900 || arg2 == 0x1000) { > printf("%x %x\n", arg1, arg2) > } > } > 1M skb alloc/free 484280 (usecs)
Real life scripts, for examples the ones related to network protocol analysis will often have such patterns in them, so I don't think this measurement is particularly unfair.
Thanks,
Ingo
| |