console stops with 9.1-RELEASE when under forwarding load

[Kurt Lidl]

On Wed, Jan 23, 2013 at 11:30:09PM +0100, Marius Strobl wrote:
> On Mon, Jan 21, 2013 at 11:35:41PM -0500, Kurt Lidl wrote:
> > I'm not sure if this is better directed at freebsd-sparc64@
> > or freebsd-net@ but I'm going to guess here...
> > 
> > Anyways.  In all cases, I'm using an absolutely stock
> > FreeBSD 9.1-release installation.
> > 
> > I got several SunFire V120 machines recently, and have been testing
> > them out to verify their operation.  They all started out identically
> > configured -- 1 GB of memory, 2x36GB disks, DVD-rom, 650Mhz processor.
> > The V120 has two on-board "gem" network interfaces.  And the machine
> > can take a single, 32-bit PCI card.
> > 
> > I've benchmarked the gem interfaces being able to source or sink
> > about 90mbit/sec of TCP traffic.  This is comparable to the speed
> > of "hme" interfaces that I've tested in my slower Netra-T1-105
> > machines.
> > 
> > So.  I put a Intel 32bit gig-e interface (a "GT" desktop
> > Gig-E interface) into the machine, and it comes up like this:
> > 
> > em0: <Intel(R) PRO/1000 Legacy Network Connection 1.0.4> port 0xc00200-0xc0023f mem 0x20000-0x3ffff,0x40000-0x5ffff at device 5.0 on pci2
> > em0: Memory Access and/or Bus Master bits were not set!
> > em0: Ethernet address: 00:1b:21:<redacted>
> > 
> > That interface can source or sink TCP traffic at about
> > 248 mbit/sec.
> > 
> > Since I really want to make one of these machines my firewall/router,
> > I took a different, dual-port Intel Gig-E server adaptor (a 64bit
> > PCI card) and put it into one of the machines so I could look at
> > the fowarding performance.  It probes like this:
> > 
> > em0: <Intel(R) PRO/1000 Legacy Network Connection 1.0.4> port 0xc00200-0xc0023f mem 0x20000-0x3ffff,0x40000-0x7ffff at device 5.0 on pci2
> > em0: Memory Access and/or Bus Master bits were not set!
> > em0: Ethernet address: 00:04:23:<redacted>
> > em1: <Intel(R) PRO/1000 Legacy Network Connection 1.0.4> port 0xc00240-0xc0027f mem 0xc0000-0xdffff,0x100000-0x13ffff at device 5.1 on pci2
> > em1: Memory Access and/or Bus Master bits were not set!
> > em1: Ethernet address: 00:04:23:<redacted>
> > 
> > Now this card can source traffic at about 250 mbit/sec and can sink
> > traffic around 204 mbit/sec.
> > 
> > But the real question is - how is the forwarding performance?
> > 
> > So I setup a test between some machines:
> > 
> > A --tcp data--> em0-sparc64-em1 --tcp data--> B
> > |                                             |
> > \---------<--------tcp acks-------<-----------/
> > 
> > So, A sends to interface em0 on the sparc64, the sparc64
> > forward out em1 to host B, and the ack traffic flows out
> > a different interface from B to A.  (A and B are amd64
> > machines, with Gig-E interfaces that are considerably
> > faster than the sparc64 machines.)
> > 
> > This test works surprisingly well -- 270 mbit/sec of forwarding
> > traffic, at around 29500 packets/second.
> > 
> > The problem is when I change the test to send the tcp ack traffic
> > back through the sparc64 (so, ack traffic goes from B into em1,
> > then forwarded out em0 to A), while doing the data in the same way.
> > 
> > The console of the sparc64 becomes completely unresponsive during
> > the running of this test.  The 'netstat 1' that I been running just
> > stops.  When the data finishes transmitting, the netstat output
> > gives one giant jump, counting all the packets that were sent during
> > the test as if they happened in a single second.
> > 
> > It's pretty clear that the process I'm running on the console isn't
> > receiving any cycles at all.  This is true for whatever I have
> > running on the console of machine -- a shell, vmstat, iostat,
> > whatever.  It just hangs until the forwarding test is over.
> > Then the console input/output resumes normally.
> > 
> > Has anybody else seen this type of problem?
> > 
> 
> I don't see what could be a sparc64-specific problem in this case.
> You are certainly pushing the hardware beyond its limits though and
> it would be interesting to know how a similarly "powerful" i386
> machine behaves in this case.
> In any case, in order to not burn any CPU cycles needlessly, you
> should use a kernel built from a config stripped down to your
> requirements and with options SMP removed to get the maximum out
> of a UP machine. It could also be that SCHED_ULE actually helps
> in this case (there's a bug in 9.1-RELEASE causing problems with
> SCHED_ULE and SMP on sparc64, but for UP it should be fine).

I updated the kernel tree on one of my sparc64 machines to the
latest version of 9-STABLE, and gave the following combinations a
try:
	SMP+ULE
	SMP+4BSD
	non-SMP+ULE
	non-SMP+4BSD
They all performed about the same, in terms of throughput,
and about the same in terms of user-responsiveness when under load.
None were responsive when forwarding ~214mbit/sec of traffic.

I played around a bit with tuning of the rx/tx queue depths for the
em0/em1 devices, but none of that had any perceptable difference in
the level of throughput or responsiveness of the machine.

-Kurt