I reported one of the duplicates that you've merged. I still see this warning running 2.6.31-19-server (x86_64).

I have a feeling this is related, in my case, to bittorrent traffic. This box is a NAS and SAN serving several diskless boxes over iSCSI, NFS and CIFS, and its gigabit NIC sees a LOT of traffic all the time. However I hadn't seen this warning for over a month. Last week I downloaded and seeded at decent speeds (10-20Mbps) several distro DVDs, and I got three of these warnings in three days, all implicating the 100Mbps NIC. It's all circumstantial, but could be a clue as to the root cause.

Feb 22 19:15:44 nas kernel: [ 9062.040017] ------------[ cut here ]------------
Feb 22 19:15:44 nas kernel: [ 9062.040027] WARNING: at /build/buildd/linux-2.6.31/net/sched/sch_generic.c:246 dev_watchdog+0x262/0x270()
Feb 22 19:15:44 nas kernel: [ 9062.040030] Hardware name: GA-MA770-US3
Feb 22 19:15:44 nas kernel: [ 9062.040032] NETDEV WATCHDOG: eth1 (8139too): transmit queue 0 timed out
Feb 22 19:15:44 nas kernel: [ 9062.040034] Modules linked in: binfmt_misc ppdev iscsi_trgt crc32c ib_iser rdma_cm ib_cm iw_cm ib_sa ib_mad ib_core ib_addr iscsi_tcp nfsd libiscsi_tcp libiscsi scsi_transport_iscsi nfs lockd nfs_acl auth_rpcgss sunrpc iptable_filter ip_tables x_tables i2c_piix4 serio_raw lp amd64_edac_mod edac_core k8temp parport xfs exportfs raid10 raid456 raid6_pq async_xor async_memcpy async_tx xor raid1 raid0 multipath 8139too 8139cp linear r8169 mii
Feb 22 19:15:44 nas kernel: [ 9062.040066] Pid: 0, comm: swapper Not tainted 2.6.31-19-server #56-Ubuntu
Feb 22 19:15:44 nas kernel: [ 9062.040068] Call Trace:
Feb 22 19:15:44 nas kernel: [ 9062.040070]  <IRQ>  [<ffffffff8105e508>] warn_slowpath_common+0x78/0xb0
Feb 22 19:15:44 nas kernel: [ 9062.040079]  [<ffffffff8105e59c>] warn_slowpath_fmt+0x3c/0x40
Feb 22 19:15:44 nas kernel: [ 9062.040082]  [<ffffffff8144e322>] dev_watchdog+0x262/0x270
Feb 22 19:15:44 nas kernel: [ 9062.040086]  [<ffffffff8107c471>] ? ktime_get_ts+0x51/0x70
Feb 22 19:15:44 nas kernel: [ 9062.040090]  [<ffffffff8103435f>] ? hpet_msi_next_event+0xf/0x20
Feb 22 19:15:44 nas kernel: [ 9062.040094]  [<ffffffff8108506f>] ? clockevents_program_event+0x4f/0x90
Feb 22 19:15:44 nas kernel: [ 9062.040097]  [<ffffffff81086560>] ? tick_dev_program_event+0x40/0xd0
Feb 22 19:15:44 nas kernel: [ 9062.040100]  [<ffffffff8144e0c0>] ? dev_watchdog+0x0/0x270
Feb 22 19:15:44 nas kernel: [ 9062.040103]  [<ffffffff8106a7fc>] run_timer_softirq+0x16c/0x270
Feb 22 19:15:44 nas kernel: [ 9062.040107]  [<ffffffff810650ed>] __do_softirq+0xbd/0x200
Feb 22 19:15:44 nas kernel: [ 9062.040111]  [<ffffffff810131ac>] call_softirq+0x1c/0x30
Feb 22 19:15:44 nas kernel: [ 9062.040113]  [<ffffffff81014b85>] do_softirq+0x55/0x90
Feb 22 19:15:44 nas kernel: [ 9062.040116]  [<ffffffff81064e55>] irq_exit+0x85/0x90
Feb 22 19:15:44 nas kernel: [ 9062.040119]  [<ffffffff810140c0>] do_IRQ+0x70/0xe0
Feb 22 19:15:44 nas kernel: [ 9062.040123]  [<ffffffff810129d3>] ret_from_intr+0x0/0x11
Feb 22 19:15:44 nas kernel: [ 9062.040124]  <EOI>  [<ffffffff810356f6>] ? native_safe_halt+0x6/0x10
Feb 22 19:15:44 nas kernel: [ 9062.040130]  [<ffffffff8101a0fc>] ? default_idle+0x4c/0xe0
Feb 22 19:15:44 nas kernel: [ 9062.040133]  [<ffffffff8101a1ee>] ? c1e_idle+0x5e/0x120
Feb 22 19:15:44 nas kernel: [ 9062.040137]  [<ffffffff81010e02>] ? cpu_idle+0xb2/0x100
Feb 22 19:15:44 nas kernel: [ 9062.040140]  [<ffffffff81512c36>] ? rest_init+0x66/0x70
Feb 22 19:15:44 nas kernel: [ 9062.040144]  [<ffffffff81838047>] ? start_kernel+0x352/0x35b
Feb 22 19:15:44 nas kernel: [ 9062.040148]  [<ffffffff8183759a>] ? x86_64_start_reservations+0x125/0x129
Feb 22 19:15:44 nas kernel: [ 9062.040151]  [<ffffffff81837698>] ? x86_64_start_kernel+0xfa/0x109
Feb 22 19:15:44 nas kernel: [ 9062.040153] ---[ end trace 58f80f6497633a24 ]---