linux-kernel - Re: [PATCH] bpf: Update sysctl documentation to list all supported architectures

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Date:   Wed, 16 Aug 2017 15:29:02 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Michael Ellerman <mpe@...erman.id.au>, ast@...nel.org
CC:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: Update sysctl documentation to list all supported
 architectures

On 08/16/2017 01:10 PM, Michael Ellerman wrote:
> Daniel Borkmann <daniel@...earbox.net> writes:
>> On 08/16/2017 07:15 AM, Michael Ellerman wrote:
>>> The sysctl documentation states that the JIT is only available on
>>> x86_64, which is no longer correct.
>>>
>>> Update the list to include all architectures that enable HAVE_CBPF_JIT
>>> or HAVE_EBPF_JIT under some configuration.
>>>
>>> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
>>
>> Thanks for the patch!
>>
>>>    Documentation/sysctl/net.txt | 5 +++--
>>>    1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt
>>> index 14db18c970b1..f68356024d09 100644
>>> --- a/Documentation/sysctl/net.txt
>>> +++ b/Documentation/sysctl/net.txt
>>> @@ -36,8 +36,9 @@ bpf_jit_enable
>>>    --------------
>>>
>>>    This enables Berkeley Packet Filter Just in Time compiler.
>>> -Currently supported on x86_64 architecture, bpf_jit provides a framework
>>> -to speed packet filtering, the one used by tcpdump/libpcap for example.
>>> +Currently supported on arm, arm64, mips, powerpc, s390, sparc and x86_64
>>> +architectures, bpf_jit provides a framework to speed packet filtering, the one
>>> +used by tcpdump/libpcap for example.
>>
>> Good point, could we actually make that as a bullet list and
>> differentiate between cBPF and eBPF JITs, so that a user doesn't
>> need to run git grep HAVE_{E,C}BPF_JIT to figure it out what the
>> switch enables on the arch used? That would be great.
>
> We could.
>
> Does a user of the sysctl want/need to know the difference though? Or do
> they just want to turn on "the JIT"?

They would just turn it on, but I think it would be nice to inform
them which archs support eBPF (which is a superset of cBPF in term
of what can be jited), so in case they have some native eBPF programs
they would see whether these can also be jited.