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Re: Enabling linux kernel jit compiler from dumpcap?
From: Bálint Réczey <balint () balintreczey hu>
Date: Fri, 23 Aug 2013 10:50:21 +0200

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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