Wireshark · Wireshark-dev: Re: [Wireshark-dev] Enabling linux kernel jit compiler from dumpcap?

[Bálint Réczey <balint@xxxxxxxxxxxxxxx>]

Hi,

2013/8/23 Anders Broman <a.broman@xxxxxxxxxxxx>:
> Bálint Réczey skrev 2013-08-22 23:02:
...
>> Regarding Wireshark I would prefer suggesting "echo 1 >
>> /proc/sys/net/core/bpf_jit_enable" in the documentation
>> instead of adding code to enable JIT.
>> There may be good reasons for not enabling it by default in the Linux
>> kernel.
>
> The problematic thing is that people seldom reads the documentation, the
> setting gets reset at a reboot
> and it's easy to forget to re-enable it. The ideal thing would be if dumpcap
For people not reading the documentation capturing will be a bit
slower or we could
put a note on the welcome screen if JIT is not enabled.
For persistently enabling JIT we could also mention Sysfsutils [1].

> - Had a preference/command line flag whether to use JIT or not.
> - If told to use it check if it was enabled or not used JIT and put it back
> to zero if not set when starting.
I would prefer not adding features which can be implemented easily
with two lines of scripts
or with a change in the system configuration.

> Wireshark could then default to use JIT and some warnings could be displayed
> in the welcome screen
> and in dumpcaps help output.
>
> netsniff-ng activates it by default it seems.
I think it is not very kind of them.

Cheers,
Balint

> Regards
> Anders
>
>>
>> Cheers,
>> Balint
>>
>> 2013/8/22 Anders Broman <a.broman@xxxxxxxxxxxx>:
>>>
>>> Guy Harris skrev 2013-08-22 18:16:
>>>
>>>> On Aug 22, 2013, at 4:46 AM, Anders Broman <anders.broman@xxxxxxxxxxxx>
>>>> wrote:
>>>>
>>>>> Should we add code to enable the JIT compiler from dumpcap?
>>>>
>>>> Should I add code to enable the JIT compiler to libpcap while I'm at it?
>>>>
>>>> Should the Linux kernel folks enable it by default?
>>>>
>>>> I'm inclined to answer "yes" to all three questions.  I think the
>>>> FreeBSD
>>>> JIT compiler is enabled by default.  I'm surprised that the Linux one
>>>> isn't.
>>>
>>> I checked in the dumpcap code. I agree that it might be useful in libpcap
>>> too, root privileges are required to
>>> change it I think. and Yes
>>>
>>>> I'm surprised that the Linux one isn't
>>>
>>> Regards
>>> Anders
>>>
>>>>

[1] http://linux-diag.sourceforge.net/Sysfsutils.html