HAS_PCAP_IMMEDIATE_MODE for TPACKET_V3

[MerinoSheep]

Question

I believe I discoverd a potential Linux performance regression linked to the code cleanup in #1772. Forcing pcap_set_immediate_mode causes libpcap to fall back from TPACKET_V3 to TPACKET_V2 in this part of the code

PcapPlusPlus/Pcap++/src/PcapLiveDevice.cpp

Line 679 in 80c7328

#ifdef HAS_PCAP_IMMEDIATE_MODE

In my initial testing, disabling immediate mode significantly reduced CPU usage and increased throughput under load. I wanted to confirm what the intended behavior is currently. Thanks.

Relevant libpcap code

Operating systems

No response

[Dimi1010]

I am unsure if we have a requirement that needs it forced on.
From what I can see in the libpcap source, it only uses tpacket_v2 if the switch is enabled.

I think the cleanest way to address this is to add a immediate mode switch added to DeviceConfiguration, so the user can choose.
I am unsure on what the default value to be. Possibly default it to ON to keep the current behavior with previous versions?

[MerinoSheep]

Yeah that sounds good, I can make a PR for this then if needed.

[Dimi1010]

Sure. Go for it.