netdev - Re: [PATCH v2] PPC: bpf_jit_comp: add SKF_AD

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Date:	Sat, 01 Nov 2014 19:31:37 +0100
From:	Daniel Borkmann <dborkman@...hat.com>
To:	David Miller <davem@...emloft.net>
CC:	kda@...ux-powerpc.org, alexei.starovoitov@...il.com,
	netdev@...r.kernel.org, linuxppc-dev@...abs.org,
	mpe@...erman.id.au, matt@...abs.org
Subject: Re: [PATCH v2] PPC: bpf_jit_comp: add SKF_AD_PKTTYPE instruction

On 11/01/2014 07:00 PM, David Miller wrote:
> From: Denis Kirjanov <kda@...ux-powerpc.org>
> Date: Sat, 1 Nov 2014 21:49:27 +0400
>
>> David, you need a feedback from other guys to apply this patch, right?
>>
>> Alexei wanted some output before/after the patch.
>> Michael Ellerman wanted the explanation what a BPF_ANC | SKF_AD_PKTTYPE means.

The BPF_ANC | SKF_AD_PKTTYPE case means that this is an ancillary
operation aka BPF extension which loads the value of skb->pkt_type
into the accumulator.

A similar transformation, that is, from BPF into eBPF insns can be
found in convert_bpf_extensions() in the SKF_AD_PKTTYPE case, or
commit 709f6c58d4dc ("sparc: bpf_jit: add SKF_AD_PKTTYPE support
to JIT") that recently enabled the same in sparc.

>> So I'm waiting  the ack/nack from them...
>
> I don't really think performance metrics are necessary just for adding
> SKF_AD_PKTTYPE support, that's sort of an over the top requirement
> if you ask me.

Right, lib/test_bpf.c actually brings the quoted output w/ numbers
for free. I think the important point was that the 'After:' case
with ``echo 1 > /proc/sys/net/core/bpf_jit_enable'' runs through for
that test case, which has been shown here.

> It's pretty obvious that we should support as many operations as
> possible to each JIT, because all of program has to do is use that
> unsupported opcode and then we have none of that program being JIT'd.
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