Hi,
On 27-Apr-06, at 10:38, Jeremie Le Hen wrote:
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 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.
Shortly after I opened the thread, most replies I received (from the
list or privately) were saying that a second CPU either wouldn't help
to improve the situation, or that the performance gain was unclear. We
had an immediate problem to solve and the management wasn't comfortable
in throwing money at new and expensive hardware that, in the end, might
or might not solve the issue.
The performance gain with fastforwarding enabled was almost 20% and
that's what we've been running since.
Note, however, that I am also using virtual interface disc0 and that
fastforwarding doesn't work with that interface (at least prior to and
including FreeBSD 6.0-release-p4). Gleb Smirnoff sent me a one-line
patch that fixed the problem.
Hope this helps.
Regards,
--
Marcos
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