em(4) receive part wedging randomly at moderate load

[Petri Helenius]

Benjamin Rosenblum wrote:

> the em driver in itself is extremly buggy.  many people, myself 
> included, are hitting some major problems with this driver that are 
> causeing some serious issues.  i cant transfer any large files to my 
> server because the em driver panics and drops the connection for 15-20 
> seconds.  its a real pain in the butt when this happens too cause this 
> is my primary network storage server.  i have had to resort to the 
> backup systems lately because of this problem.  i think the entire em 
> network driver needs to get reworked and all these bugs really need to 
> be taken care of since this is one of the top like 3 network cards 
> used in the field today for gig transfer.
>
Does anyone have the programming data for the chipsets so the driver 
could be taken further? I've been unable to obtain them from Intel 
despite of repeated attempts.

Pete

> Gleb Smirnoff wrote:
>
>>  Colleagues,
>>
>>  during last month we are experiencing a nasty problem with em(4)
>> driver. Several times a day the receive path of the driver wedges
>> for a minute or two. During wedge the transmit part works with
>> no problems. The latter fact makes this problem very nasty, because
>> the problematic router can't be backed up with help of CARP.
>>
>> Some details: during the wedge all incoming packets are lost and
>> counted as "Missed packets". I've checked this using
>> `sysctl dev.em.0.stats=1`. The `dmesg` output is the following:
>>
>> em0: Excessive collisions = 0
>> em0: Symbol errors = 0
>> em0: Sequence errors = 0
>> em0: Defer count = 0
>> em0: Missed Packets = 1266
>> em0: Receive No Buffers = 220
>> em0: Receive length errors = 0
>> em0: Receive errors = 0
>> em0: Crc errors = 0
>> em0: Alignment errors = 0
>> em0: Carrier extension errors = 0
>> em0: XON Rcvd = 0
>> em0: XON Xmtd = 0
>> em0: XOFF Rcvd = 0
>> em0: XOFF Xmtd = 0
>> em0: Good Packets Rcvd = 28347789
>> em0: Good Packets Xmtd = 30911959
>>
>> There is a clear evidence that command `sysctl dev.em.0.stats=1` itself
>> can trigger the wedge. It is important, that the stats are printed
>> to a 9600 baud serial console, and this takes about a second. I have
>> suspicion, that the wedge happens when kernel doesn't service NIC
>> interrupts for some period of time. Yes, some packets should be lost in
>> this case, but the wedge must not continue for minutes!
>>
>> The box is serving 8 - 15 kpps, 70 - 100 MBps. It runs stateful pf(4)
>> firewall, with 50k - 80k states. The IP fastforwarding is enabled. The
>> average state insert/removal ratio is 300 states per second, however
>> sometimes several thousands of states can be removed in one pass. The
>> state removal locks the network code for quite a long time, so I guess
>> that wedge happens exactly when a lot of states are removed. The NIC
>> interrupts aren't serviced for some time and it wedges.
>>
>> The hardware is Supermicro server, with two onboard NICs:
>> dev.em.0.%pnpinfo: vendor=0x8086 device=0x1075 subvendor=0x8086 
>> subdevice=0x1075 class=0x020000
>> dev.em.1.%pnpinfo: vendor=0x8086 device=0x1076 subvendor=0x8086 
>> subdevice=0x1076 class=0x020000
>>
>> The NIC is plugged in Cisco Catalyst 6509 gigabit ethernet port. No
>> errors are counted on switch port.
>>
>> To workaround the problem, I have made the following patch:
>>
>> @@ -1650,12 +1651,18 @@
>>        struct ifnet   *ifp;
>>        struct adapter * adapter = arg;
>>        ifp = adapter->ifp;
>> +       uint64_t        ompc;
>>
>>        EM_LOCK(adapter);
>>
>>        em_check_for_link(&adapter->hw);
>>        em_print_link_status(adapter);
>> -       em_update_stats_counters(adapter);   +       ompc = 
>> adapter->stats.mpc;
>> +       em_update_stats_counters(adapter);
>> +       if (adapter->stats.mpc > ompc) {
>> +               printf("em watchdog: mpc %lld->%lld\n", ompc, 
>> adapter->stats.mpc);
>> +               em_init_locked(adapter);
>> +       }
>>        if (em_display_debug_stats && ifp->if_drv_flags & 
>> IFF_DRV_RUNNING) {
>>                em_print_hw_stats(adapter);
>>        }
>>
>> It helps to reduce downtime from few minutes to 2 seconds, but this
>> is very dirty approach to the problem. Sample prints during runtime
>> with patch:
>>
>> em watchdog: mpc 1767->2739
>> em watchdog: mpc 2739->4724
>> em watchdog: mpc 4724->7794
>> em watchdog: mpc 7794->10729
>>
>> Every time this is printed, the network wedges for 2 seconds and then
>> it revives.
>>
>> I am asking developers, who work in Intel, to pay attention to this 
>> problem.
>>
>>> From my side I can offer any help in testing and debugging.
>>
>>
>>  
>>
>
>
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