On Thu, Dec 5, 2013 at 12:40 PM, Alexei Starovoitov <a...@plumgrid.com> wrote:
>> On Tue, Dec 3, 2013 at 4:01 PM, Andi Kleen <a...@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)
>
I've lost my mind for a while. :)
If bpf only focus on filter, then it's not good to compare with ktap
like that, since
ktap can easily make use on current kernel filter, you should use below script:
trace skb:kfree_skb /location == 0x100 || location == 0x200 || .../ {
printf("%x %x\n", arg1, arg2)
}
As ktap is a user of current simple kernel tracing filter, I fully
agree with Steven,
"it can be an add on, but not a replacement."
Thanks,
Jovi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
