From: Daniel Borkmann <dborkman@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Chema Gonzalez <chema@google.com>,
David Miller <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
netdev@vger.kernel.org, ast@plumgrid.com
Subject: Re: [PATCH] filter: added BPF random opcode
Date: Tue, 15 Apr 2014 17:04:18 +0200 [thread overview]
Message-ID: <534D4A72.2010909@redhat.com> (raw)
In-Reply-To: <1397572894.4222.98.camel@edumazet-glaptop2.roam.corp.google.com>
On 04/15/2014 04:41 PM, Eric Dumazet wrote:
> On Tue, 2014-04-15 at 09:24 +0200, Daniel Borkmann wrote:
>
>>> @@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
>>> case SKF_AD_OFF + SKF_AD_NLATTR:
>>> case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
>>> case SKF_AD_OFF + SKF_AD_CPU:
>>> + case SKF_AD_OFF + SKF_AD_RANDOM:
>>
>> I think instead of a function call, this sould rather be modelled
>> directly into the internal insn set and thus converted differently,
>> so we can spare us the call.
>
> Hmmm... this would need percpu storage, thus preempt disable/enable
> calls, and prandom_u32_state() is about 40 instructions.
>
> This is really not worth the pain.
Absolutely, that was not what I meant actually. Calling to
prandom_u32_state() is fine, no need to have another prng just
for that. I was just wondering if it makes sense to model that
directly as an instruction into a jump-table target that calls
prandom_u32() from there instead 'indirectly'. Need to think
about this a bit more ...
next prev parent reply other threads:[~2014-04-15 15:04 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-14 23:02 [PATCH] filter: added BPF random opcode Chema Gonzalez
2014-04-15 7:24 ` Daniel Borkmann
2014-04-15 14:41 ` Eric Dumazet
2014-04-15 15:04 ` Daniel Borkmann [this message]
2014-04-15 16:22 ` Chema Gonzalez
2014-04-15 16:30 ` Chema Gonzalez
2014-04-15 16:44 ` Daniel Borkmann
2014-04-15 18:19 ` Chema Gonzalez
-- strict thread matches above, loose matches on Subject: below --
2014-04-15 18:16 Chema Gonzalez
2014-04-16 6:24 ` Alexei Starovoitov
2014-04-16 8:32 ` Daniel Borkmann
2014-04-17 0:19 ` Chema Gonzalez
2014-04-17 1:38 ` Eric Dumazet
2014-04-18 20:21 ` Alexei Starovoitov
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