Really slow gigabit link in one direction (em -> sk)

Hiho! :-)

Transfer speed from the em adapter in our fileserver to another machine
(sk adapter) is really slow (measurements taken with iperf without
options):

------------------------------------------------------------
Client connecting to 192.168.0.23, TCP port 5001
TCP window size: 32.5 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.222 port 52856 connected with 192.168.0.23 port
5001 [ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.2 sec    181 MBytes    149 Mbits/sec

On the other hand, speed from the sk adapter to em is acceptable (for
an untuned connection and a possibly crappy cable, imho):

------------------------------------------------------------
Client connecting to 192.168.0.222, TCP port 5001
TCP window size: 32.5 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.23 port 32579 connected with 192.168.0.222 port
5001 [ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec    505 MBytes    423 Mbits/sec



Cable is about 15m long, cat-5. On the receiving end sits a Marvell sk
gigabit card. I've tried setting the mtu on both sides to 9000 and to
other values as well, but it makes no difference. Neither does
increasing 

net.inet.tcp.sendspace: 32768
net.inet.tcp.recvspace: 65536

to 8MB, as some sources suggested (actually, it does make a difference,
it nets ca. 100Mbit more in the sk->em direction, but does nothing for
the em->sk direction). Am I doing something wrong? Should I burn my
cable? :-)


Additional info for the machine containing the sk card:

skc0_at_pci0:2:8:0: class=0x020000 card=0xc2311297 chip=0x432011ab
rev=0x13 hdr=0x00 vendor     = 'Marvell Semiconductor (Was: Galileo
Technology Ltd)' 
	device     = 'Yukon 88E8001/8003/8010 PCI Gigabit
		     Ethernet Controller (Copper)' 
	class      = network
 	subclass   = ethernet

sk0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500 options=b<RXCSUM,TXCSUM,VLAN_MTU>
        ether 00:30:1b:b5:fb:d9
        inet 192.168.0.23 netmask 0xffffff00 broadcast 192.168.0.255
        media: Ethernet autoselect (1000baseT <full-duplex,flag0,flag1>)
        status: active

net.inet.tcp.mssdflt: 512
net.inet.tcp.keepidle: 7200000
net.inet.tcp.keepintvl: 75000
net.inet.tcp.sendspace: 32768
net.inet.tcp.recvspace: 65536
net.inet.tcp.keepinit: 75000
net.inet.tcp.delacktime: 100
net.inet.tcp.v6mssdflt: 1024
net.inet.tcp.hostcache.purge: 0
net.inet.tcp.hostcache.prune: 300
net.inet.tcp.hostcache.expire: 3600
net.inet.tcp.hostcache.count: 310
net.inet.tcp.hostcache.bucketlimit: 30
net.inet.tcp.hostcache.hashsize: 512
net.inet.tcp.hostcache.cachelimit: 15360
net.inet.tcp.wlock_looped: 0
net.inet.tcp.wlock_relocked: 0
net.inet.tcp.wlock_upgraded: 11246
net.inet.tcp.tcp_wlock_atfirst: 19669
net.inet.tcp.rlock_atfirst: 4875339
net.inet.tcp.read_locking: 1
net.inet.tcp.recvbuf_max: 16777216
net.inet.tcp.recvbuf_inc: 16384
net.inet.tcp.recvbuf_auto: 1
net.inet.tcp.insecure_rst: 0
net.inet.tcp.ecn.maxretries: 1
net.inet.tcp.ecn.enable: 0
net.inet.tcp.abc_l_var: 2
net.inet.tcp.rfc3465: 1
net.inet.tcp.rfc3390: 1
net.inet.tcp.rfc3042: 1
net.inet.tcp.drop_synfin: 0
net.inet.tcp.delayed_ack: 1
net.inet.tcp.blackhole: 0
net.inet.tcp.log_in_vain: 0
net.inet.tcp.sendbuf_max: 16777216
net.inet.tcp.sendbuf_inc: 8192
net.inet.tcp.sendbuf_auto: 1
net.inet.tcp.tso: 1
net.inet.tcp.newreno: 1
net.inet.tcp.local_slowstart_flightsize: 4
net.inet.tcp.slowstart_flightsize: 1
net.inet.tcp.path_mtu_discovery: 1
net.inet.tcp.reass.overflows: 2610
net.inet.tcp.reass.maxqlen: 48
net.inet.tcp.reass.cursegments: 2
net.inet.tcp.reass.maxsegments: 1600
net.inet.tcp.sack.globalholes: 0
net.inet.tcp.sack.globalmaxholes: 65536
net.inet.tcp.sack.maxholes: 128
net.inet.tcp.sack.enable: 1
net.inet.tcp.inflight.stab: 20
net.inet.tcp.inflight.max: 1073725440
net.inet.tcp.inflight.min: 6144
net.inet.tcp.inflight.rttthresh: 10
net.inet.tcp.inflight.debug: 0
net.inet.tcp.inflight.enable: 1
net.inet.tcp.isn_reseed_interval: 0
net.inet.tcp.icmp_may_rst: 1
net.inet.tcp.pcbcount: 96
net.inet.tcp.do_tcpdrain: 1
net.inet.tcp.tcbhashsize: 512
net.inet.tcp.log_debug: 0
net.inet.tcp.minmss: 216
net.inet.tcp.syncache.rst_on_sock_fail: 1
net.inet.tcp.syncache.rexmtlimit: 3
net.inet.tcp.syncache.hashsize: 512
net.inet.tcp.syncache.count: 0
net.inet.tcp.syncache.cachelimit: 15360
net.inet.tcp.syncache.bucketlimit: 30
net.inet.tcp.syncookies_only: 0
net.inet.tcp.syncookies: 1
net.inet.tcp.timer_race: 0
net.inet.tcp.finwait2_timeout: 60000
net.inet.tcp.fast_finwait2_recycle: 0
net.inet.tcp.always_keepalive: 1
net.inet.tcp.rexmit_slop: 200
net.inet.tcp.rexmit_min: 30
net.inet.tcp.msl: 30000
net.inet.tcp.nolocaltimewait: 0
net.inet.tcp.maxtcptw: 5120



Additional info for the computer with the em card:

em0_at_pci0:1:7:0: class=0x020000 card=0x13768086 chip=0x107c8086 rev=0x05
hdr=0x00 vendor     = 'Intel Corporation'
    device     = 'Gigabit Ethernet Controller (Copper) rev 5 (82541PI)'
    class      = network
    subclass   = ethernet

em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
9000 options=9b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
        ether 00:1b:21:17:2e:5d
        inet 192.168.0.222 netmask 0xffffff00 broadcast 192.168.0.255
        media: Ethernet autoselect (1000baseT <full-duplex>)
        status: active

net.inet.tcp.rfc1323: 1
net.inet.tcp.mssdflt: 512
net.inet.tcp.keepidle: 7200000
net.inet.tcp.keepintvl: 75000
net.inet.tcp.sendspace: 32768
net.inet.tcp.recvspace: 65536
net.inet.tcp.keepinit: 75000
net.inet.tcp.delacktime: 100
net.inet.tcp.v6mssdflt: 1024
net.inet.tcp.hostcache.purge: 0
net.inet.tcp.hostcache.prune: 300
net.inet.tcp.hostcache.expire: 3600
net.inet.tcp.hostcache.count: 1
net.inet.tcp.hostcache.bucketlimit: 30
net.inet.tcp.hostcache.hashsize: 512
net.inet.tcp.hostcache.cachelimit: 15360
net.inet.tcp.wlock_looped: 0
net.inet.tcp.wlock_relocked: 0
net.inet.tcp.wlock_upgraded: 281
net.inet.tcp.tcp_wlock_atfirst: 296
net.inet.tcp.rlock_atfirst: 1608326
net.inet.tcp.read_locking: 1
net.inet.tcp.recvbuf_max: 16777216
net.inet.tcp.recvbuf_inc: 16384
net.inet.tcp.recvbuf_auto: 1
net.inet.tcp.insecure_rst: 0
net.inet.tcp.ecn.maxretries: 1
net.inet.tcp.ecn.enable: 0
net.inet.tcp.abc_l_var: 2
net.inet.tcp.rfc3465: 1
net.inet.tcp.rfc3390: 1
net.inet.tcp.rfc3042: 1
net.inet.tcp.drop_synfin: 0
net.inet.tcp.delayed_ack: 1
net.inet.tcp.blackhole: 0
net.inet.tcp.log_in_vain: 0
net.inet.tcp.sendbuf_max: 16777216
net.inet.tcp.sendbuf_inc: 8192
net.inet.tcp.sendbuf_auto: 1
net.inet.tcp.tso: 1
net.inet.tcp.newreno: 1
net.inet.tcp.local_slowstart_flightsize: 4
net.inet.tcp.slowstart_flightsize: 1
net.inet.tcp.path_mtu_discovery: 1
net.inet.tcp.reass.overflows: 0
net.inet.tcp.reass.maxqlen: 48
net.inet.tcp.reass.cursegments: 0
net.inet.tcp.reass.maxsegments: 1600
net.inet.tcp.sack.globalholes: 0
net.inet.tcp.sack.globalmaxholes: 65536
net.inet.tcp.sack.maxholes: 128
net.inet.tcp.sack.enable: 1
net.inet.tcp.inflight.stab: 20
net.inet.tcp.inflight.max: 1073725440
net.inet.tcp.inflight.min: 6144
net.inet.tcp.inflight.rttthresh: 10
net.inet.tcp.inflight.debug: 0
net.inet.tcp.inflight.enable: 1
net.inet.tcp.isn_reseed_interval: 0
net.inet.tcp.icmp_may_rst: 1
net.inet.tcp.pcbcount: 11
net.inet.tcp.do_tcpdrain: 1
net.inet.tcp.tcbhashsize: 512
net.inet.tcp.log_debug: 0
net.inet.tcp.minmss: 216
net.inet.tcp.syncache.rst_on_sock_fail: 1
net.inet.tcp.syncache.rexmtlimit: 3
net.inet.tcp.syncache.hashsize: 512
net.inet.tcp.syncache.count: 0
net.inet.tcp.syncache.cachelimit: 15360
net.inet.tcp.syncache.bucketlimit: 30
net.inet.tcp.syncookies_only: 0
net.inet.tcp.syncookies: 1
net.inet.tcp.timer_race: 0
net.inet.tcp.finwait2_timeout: 60000
net.inet.tcp.fast_finwait2_recycle: 0
net.inet.tcp.always_keepalive: 1
net.inet.tcp.rexmit_slop: 200
net.inet.tcp.rexmit_min: 30
net.inet.tcp.msl: 30000
net.inet.tcp.nolocaltimewait: 0
net.inet.tcp.maxtcptw: 5120


Bye
Marc

-- 
"And what rough beast, its hour come round at last,
Slouches towards Bethlehem to be born?"

W.B. Yeats, The Second Coming