Re: Question about CPU affinity for interrupts

[Livio Ricciulli <livio () metaflows com>]

The driver usually copies the packets from the NIC to the memory of the 
node (or hardware thread) where the IRQ' affinity is mapped.

If you do
numactl --hardware

You will see your memory architecture.
I am guessing all nodes use the same memory in your case; if so, I would 
map the IRQ to the free CPUs. If not, see below:

If your NIC driver/chipset can do symmetric RSS, then you would want to 
map each interrupt to a node with the smallest distance to the node 
where Snort will consume the packets from that IRQ. If your NIC cannot 
do RSS, it does not matter since the packets from each interrupt will be 
consumed by all Snort processes.

Livio.

On 03/10/2014 07:38 PM, Roger Campbell wrote:
> Hi everyone, had a question about IRQs and PF_RING.
>
> Currently I'm testing out PF_RING and snort 2.9.6 on a 1Gb/s link that 
> usually tops out around 800Mb/s.  The system has 16 physical cores (32 
> Hyper-Threads).
>
> If I run 8 snort instances in the format below, load is handled pretty 
> well.
>
> snort -R 1 --daq-dir=/usr/local/lib/daq --daq pfring --daq-mode 
> passive --daq-var clusterid=10 --daq-var bindcpu=4 -c 
> /IDS/snort/etc/snort.conf -l /IDS/snort/log1 -u snort -g snort -i eth4 -D
> snort -R 2 --daq-dir=/usr/local/lib/daq --daq pfring --daq-mode 
> passive --daq-var clusterid=10 --daq-var bindcpu=6 -c 
> /IDS/snort/etc/snort.conf -l /IDS/snort/log2 -u snort -g snort -i eth4 -D
> (continues using CPU 8,10,12,14,16,18)
>
> I know that I should set CPU affinity for interrupts for each rx queue 
> to a specific CPU or set of CPUs.  My question is, should I bind these 
> to 8 free cores, or should I bind them to cores which are already 
> hosting a snort process?
>
> All of the IRQs are currently being processed by ksoftirqd/0 on CPU 0 
> which is not optimal.
>
>
>
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