Re: Enabling linux kernel jit compiler from dumpcap?

[Bálint Réczey <balint () balintreczey hu>]

Hi,

2013/8/23 Anders Broman <a.broman () bredband net>:
> 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 () bredband net>:
> > > Guy Harris skrev 2013-08-22 18:16:
> > >
> > > > On Aug 22, 2013, at 4:46 AM, Anders Broman <anders.broman () ericsson com>
> > > > 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
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