Re: [fbsd] Re: [fbsd] Network performance in a dual CPU system

Hi, Robert,

On Thu, Apr 27, 2006 at 02:54:21PM +0100, Robert Watson wrote:

On Thu, 27 Apr 2006, Jeremie Le Hen wrote:

PID USERNAME THR PRI NICE SIZE RES STATE TIME WCPU COMMAND
60 root 1 -44 -163 0K 8K WAIT 355.6H 72.17% swi1:
net
39 root 1 -68 -187 0K 8K WAIT 52.3H 5.22% irq28:
bge0
40 root 1 -68 -187 0K 8K WAIT 28.3H 2.25% irq29:
bge1
11 root 1 171 52 0K 8K RUN 166.6H 0.00% idle
63 root 1 -16 0 0K 8K - 121:55 0.00% yarrow
61 root 1 -32 -151 0K 8K WAIT 46:21 0.00% swi4:
clock sio
[...]

Does anyone know whether a dual CPU system can help us improve the
situation? I was wondering if the software interrupt threads would be
divided between the two processors.

I am a few weeks late, I just saw this very interesting thread. What
solution did you finally employ to circumvent your high interrupt load ?

I missed the original thread, but in answer to the question: if you set
net.isr.direct=1, then FreeBSD 6.x will run the netisr code in the ithread
of the network device driver. This will allow the IP forwarding and
related paths in two threads instead of one, potentially allowing greater
parallelism. Of course, you also potentially contend more locks, you may
increase the time it takes for the ithread to respond to new interrupts,
etc, so it's not quite cut and dry, but with a workload like the one shown
above, it might make quite a difference.

Actually you already replied in the original thread, explaining mostly
the same thing. The whole thread [1] brought up multiple valuable
network performance tuning knobs, such as polling, fastforwarding,
net.isr.direct but there is no happy end to the thread. Given this is
a real world situation, I wanted to know how Marcos revolved his
problem.

BTW, what I understand is that net.isr.direct=1 prevents from
multiplexing all packets on the netisr thread and instead makes the
ithread do the job. In this case, what happens to the netisr thread ?
Does it still have some work to do or is it removed ?


Thank you.
Regards,

[1] http://lists.freebsd.org/pipermail/freebsd-net/2006-February/thread.html#9725
--
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >
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