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

From: Anders Broman <anders.broman@xxxxxxxxxxxx>
Date: Fri, 23 Aug 2013 10:23:32 +0000
> 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.

Regards
Anders 

-----Original Message-----
From: wireshark-dev-bounces@xxxxxxxxxxxxx [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Martin Kaiser
Sent: den 23 augusti 2013 10:36
To: wireshark-dev@xxxxxxxxxxxxx
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@xxxxxxxxxxxx):

> 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@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

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