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Re: Enabling linux kernel jit compiler from dumpcap?
From: Anders Broman <anders.broman () ericsson com>
Date: Fri, 23 Aug 2013 11:15:41 +0000



-----Original Message-----
From: wireshark-dev-bounces () wireshark org [mailto:wireshark-dev-bounces () wireshark org] On Behalf Of Bálint Réczey
Sent: den 23 augusti 2013 12:59
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] Enabling linux kernel jit compiler from dumpcap?

2013/8/23 Anders Broman <anders.broman () ericsson com>:
before we change it, should we remember the previous setting and restore it when dumpcap exits?

Preferably yes but I'm not sure it's possible as I think root 
privileges are required to write to the file and I think dumpcap Drops those after starting to capture.
And in the configuration the documentation recommends dumpcap does not run as root, it has permission to capture only.

Cheers,
Balint

That's kind of my point after all these years this is still not used by every one.


Regards
Anders

-----Original Message-----
From: wireshark-dev-bounces () wireshark org 
[mailto:wireshark-dev-bounces () wireshark org] On Behalf Of Martin 
Kaiser
Sent: den 23 augusti 2013 10:36
To: wireshark-dev () wireshark org
Subject: Re: [Wireshark-dev] Enabling linux kernel jit compiler from dumpcap?

before we change it, should we remember the previous setting and restore it when dumpcap exits?

Thus wrote Anders Broman (a.broman () bredband net):

Bálint Réczey skrev 2013-08-22 23:02:
Hi,

I would be happier if the applications I run did not change kernel 
configuration without my consent.
I see your point...

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
- 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.
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.
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

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