[f-nsp] Fwd: egress queue drops

[George B.]

Actually meant for the below to go to the list:

---------- Forwarded message ----------
From: George B. <georgeb at gmail.com>
Date: Thu, Jan 13, 2011 at 9:27 AM
Subject: Re: [f-nsp] egress queue drops
To: Jared Valentine <hidden at xmission.com>


Actually, if anyone has been following the "bufferbloat" conversation
on gettys blog, it is probably better to drop packets than increase
buffers.  If you are backing up into buffers, there is congestion and
you WANT to drop packets so the flows back off.  He has noticed up to
TENS of  seconds of traffic buffering end to end along some paths
(that is cumulative buffering in all devices along the path).  This
means there is no way that TCP congestion avoidance and tuning
mechanisms can work.  You might not find out a packet was dropped for
several seconds after the fact (because of traffic buffered up ahead
of the dropped packet along the path) and at that point all TCP does
is flail.

Here's the blog:

https://gettys.wordpress.com/

Go back to the beginning of the conversation and read the comments, too.

The attitude of "every packet is precious" is causing a huge
performance degradation of end user applications and things would work
a lot more smoothly if buffers were smaller and more packets got
dropped sooner.  That would allow congestion avoidance mechanisms to
actually function.

George


On Thu, Jan 13, 2011 at 9:18 AM, Jared Valentine <hidden at xmission.com> wrote:
> If you're not leveraging any QoS (and from the looks of your "show int" it
> doesn't look like it), then you could add "buffer-sharing-full" in the
> global config.  That will release the buffers that are reserved for queues
> 1-7 and make them available to queue0, which is where all of your traffic
> currently is today.
>
> If you are leveraging QoS, or plan on doing so in the near-term, then you'll
> probably need to be a little more selective about reallocating your buffers
> using specific "qd" commands instead.
>
> Jared Valentine
> hidden at xmission.com
>
> -----Original Message-----
> From: foundry-nsp-bounces at puck.nether.net
> [mailto:foundry-nsp-bounces at puck.nether.net] On Behalf Of Frederic Jaeckel
> Sent: Thursday, January 13, 2011 9:18 AM
> To: foundry-nsp
> Subject: [f-nsp] egress queue drops
>
> Hej,
>
> I'm having a few FCX switches which display egress drops in the interface
> statistics.
>
> I'm curious how I can fix that and if I can fix that. The mentioned thing
> happens on every port of the switch and at most on the uplink ports. I set
> the symmetric flow control like that:
>        symmetric-flow-control set 1 buffers 320
>
> and the error still occurs.
>
> Maybe someone has a hunch or knows the problem? Would be nice if I could fix
> that.
>
>
>> #show int e 1/1/1
>> GigabitEthernet1/1/1 is up, line protocol is up
>>   Hardware is GigabitEthernet, address is 0024.3877.9c40 (bia
> 0024.3877.9c40)
>>   Configured speed auto, actual 1Gbit, configured duplex fdx, actual fdx
>>   Configured mdi mode AUTO, actual none
>>   Member of 5 L2 VLANs, port is tagged, port state is FORWARDING
>>   BPDU guard is Disabled, ROOT protect is Disabled
>>   Link Error Dampening is Disabled
>>   STP configured to ON, priority is level0, mac-learning is enabled
>>   Flow Control is config enabled, oper enabled, negotiation disabled
>>   mirror disabled, monitor disabled
>>   Not member of any active trunks
>>   Not member of any configured trunks
>>   No port name
>>   Inter-Packet Gap (IPG) is 96 bit times
>>   IP MTU 1500 bytes
>>   300 second input rate: 136526024 bits/sec, 41720 packets/sec, 14.31%
> utilization
>>   300 second output rate: 355122840 bits/sec, 55045 packets/sec, 36.38%
> utilization
>>   7038712 packets input, 2873484976 bytes, 0 no buffer
>>   Received 8 broadcasts, 1101 multicasts, 7037603 unicasts
>>   0 input errors, 0 CRC, 0 frame, 0 ignored
>>   0 runts, 0 giants
>>   9327790 packets output, 7548747686 bytes, 0 underruns
>>   Transmitted 16 broadcasts, 7630 multicasts, 9320144 unicasts
>>   0 output errors, 0 collisions
>>   Relay Agent Information option: Disabled
>>
>> Egress queues:
>> Queue counters    Queued packets    Dropped Packets
>>     0             9327946                1356
>>     1                   0                   0
>>     2                   0                   0
>>     3                   0                   0
>>     4                   0                   0
>>     5                   0                   0
>>     6                   0                   0
>>     7                   0                   0
>
> best regards,
> Frederic Jaeckel
>
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