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From: Edward Cree <ecree@solarflare.com>
To: Jiong Wang <jiong.wang@netronome.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
	Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Jakub Kicinski <jakub.kicinski@netronome.com>
Subject: Re: [PATCH] bpf: optimize constant blinding
Date: Mon, 17 Jun 2019 21:11:52 +0100
Message-ID: <58d86352-4989-38d6-666b-5e932df9ed46@solarflare.com> (raw)
In-Reply-To: <878su0geyt.fsf@netronome.com>

On 17/06/2019 20:59, Jiong Wang wrote:
> Edward Cree writes:
>
>> On 14/06/2019 16:13, Jiong Wang wrote:
>>> Just an update and keep people posted.
>>>
>>> Working on linked list based approach, the implementation looks like the
>>> following, mostly a combine of discussions happened and Naveen's patch,
>>> please feel free to comment.
>>>
>>>   - Use the reserved opcode 0xf0 with BPF_ALU as new pseudo insn code
>>>     BPF_LIST_INSN. (0xf0 is also used with BPF_JMP class for tail call).
>>>
>>>   - Introduce patch pool into bpf_prog->aux to keep all patched insns.
>> It's not clear to me what the point of the patch pool is, rather than just
>>  doing the patch straight away. 
> I used pool because I was thinking insn to be patched could be high
> percentage, so doing lots of alloc call is going to be less efficient? so
> allocate a big pool, and each time when creating new patch node, allocate
> it from the pool directly. Node is addressed using pool_base + offset, each
> node only need to keep offset.
Good idea; but in that case it doesn't need to be a pool of patches (storing
 their prev and next), just a pool of insns.  I.e. struct bpf_insn pool[many];
 then in orig prog when patching an insn replace it with BPF_LIST_INSN.  If
 we later decide to patch an insn within a patch, we can replace it (i.e. the
 entry in bpf_insn_pool) with another BPF_LIST_INSN pointing to some later bit
 of the pool, then we just have a little bit of recursion at linearise time.
Does that work?

-Ed

  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-12 11:32 Naveen N. Rao
2019-06-12 14:47 ` Alexei Starovoitov
2019-06-12 15:04   ` Jiong Wang
2019-06-12 15:25     ` Jiong Wang
2019-06-12 15:28       ` Alexei Starovoitov
2019-06-14 15:13         ` Jiong Wang
2019-06-14 17:05           ` Alexei Starovoitov
2019-06-14 22:28             ` Andrii Nakryiko
2019-06-17 19:47           ` Edward Cree
2019-06-17 19:59             ` Jiong Wang
2019-06-17 20:11               ` Edward Cree [this message]
2019-06-17 20:40                 ` Jiong Wang
2019-06-17 20:53                   ` Alexei Starovoitov
2019-06-17 21:01                     ` Jiong Wang
2019-06-17 21:16                   ` Edward Cree
2019-06-19 20:45                     ` Jiong Wang
2019-06-14  4:30 ` kbuild test robot

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