Date:	Fri, 02 Nov 2012 01:40:38 -0700
From:	Jeff Kirsher <tarbal@...il.com>
To:	Shawn Starr <shawn.starr@...ers.com>
CC:	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net
Subject: Re: [3.5/6.x][e1000e] - Regression - Unable to receive packets if
 MTU == 1500

On 11/01/2012 10:58 AM, Shawn Starr wrote:
> Hello network driver folks,
>
> I recently decided to reinstall my Lenovo W500 laptop and found I wasn't able 
> to get DHCP leases, I wasn't able to install over PXE (when getting the IP a 
> second time within the OS)
>
> Fedora is currently using kernel-3.6.2-2.fc18.x86_64 (Pre-beta)
>
> The only difference I noticed was in my old install of Fedora, I had added 
> MTU=9000 to the interface config while using a 3.5 kernel, not knowing 3.6.x 
> seems to break things.
>
> My Cisco DPC3825 Switch/Cable modem has an MTU setting but this is from Cable 
> provider <-> WAN interface only. I tried changing to 1500 but by default it 
> uses this anyway.
>
> I had noticed tx unit hang errors sometimes, but not when MTU is above 1500.
>
> PCI info:
>
> 00:19.0 Ethernet controller: Intel Corporation 82567LM Gigabit Network 
> Connection (rev 03)
>         Subsystem: Lenovo Device 20ee
>         Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- 
> Stepping- SERR+ FastB2B- DisINTx+
>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- 
> <TAbort- <MAbort- >SERR- <PERR- INTx-
>         Latency: 0
>         Interrupt: pin A routed to IRQ 46
>         Region 0: Memory at fc000000 (32-bit, non-prefetchable) [size=128K]
>         Region 1: Memory at fc025000 (32-bit, non-prefetchable) [size=4K]
>         Region 2: I/O ports at 1840 [size=32]
>         Capabilities: [c8] Power Management version 2
>                 Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA 
> PME(D0+,D1-,D2-,D3hot+,D3cold+)
>                 Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=1 PME-
>         Capabilities: [d0] MSI: Enable+ Count=1/1 Maskable- 64bit+
>                 Address: 00000000fee0100c  Data: 41a2
>         Capabilities: [e0] PCI Advanced Features
>                 AFCap: TP+ FLR+
>                 AFCtrl: FLR-
>                 AFStatus: TP-
>         Kernel driver in use: e1000e
>
> e1000e conversation log:
>
> [   12.653816] e1000e: Intel(R) PRO/1000 Network Driver - 2.0.0-k
> [   12.653819] e1000e: Copyright(c) 1999 - 2012 Intel Corporation.
> [   12.653855] e1000e 0000:00:19.0: setting latency timer to 64
> [   12.653938] e1000e 0000:00:19.0: Interrupt Throttling Rate (ints/sec) set 
> to dynamic conservative mode
> [   12.653980] e1000e 0000:00:19.0: irq 46 for MSI/MSI-X
> [   12.844121] e1000e 0000:00:19.0: eth0: (PCI Express:2.5GT/s:Width x1) 
> 00:22:68:0c:96:e3
> [   12.844124] e1000e 0000:00:19.0: eth0: Intel(R) PRO/1000 Network Connection
> [   12.844150] e1000e 0000:00:19.0: eth0: MAC: 7, PHY: 8, PBA No: 1008FF-0FF
> [   17.459570] e1000e 0000:00:19.0: eth0: changing MTU from 1500 to 9000
> [   17.459577] e1000e 0000:00:19.0: Interrupt Throttle Rate turned off
> [   17.948121] e1000e 0000:00:19.0: irq 46 for MSI/MSI-X
> [   18.049164] e1000e 0000:00:19.0: irq 46 for MSI/MSI-X
> [   20.442936] e1000e: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow 
> Control: Rx/Tx
>
> When I set MTU = 1500 (2000 works), it will stop receiving packets, it also 
> disables Interrupt Throttling when MTU is set higher.
>
> After testing reasons why it wasn't get a DHCP lease, I decided to bump the 
> MTU to 9000 for Jumbo Frames and as soon as I did this, I was able to get a 
> lease and the network functioned resumes receiving packets.
>
> Can anyone else report regressions or might know whats going on?
>
> Thanks,
> Shawn.
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