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Re: Enabling linux kernel jit compiler from dumpcap?
From: Anders Broman <anders.broman () ericsson com>
Date: Fri, 23 Aug 2013 10:26:59 +0000

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].
I would prefer not adding features which can be implemented easily with two lines of scripts or with a change in the 
system configuration.

Could you provide patches for this alternative solution?
Regards
Anders

-----Original Message-----
From: wireshark-dev-bounces () wireshark org [mailto:wireshark-dev-bounces () wireshark org] On Behalf Of Bálint Réczey
Sent: den 23 augusti 2013 10:50
To: Anders Broman
Cc: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] Enabling linux kernel jit compiler from dumpcap?

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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