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Date:      Wed, 30 Dec 2020 19:08:03 +0300
From:      Victor Gamov <vit@otcnet.ru>
To:        Eugene Grosbein <eugen@grosbein.net>, freebsd-net@freebsd.org
Subject:   Re: 'dropped due to full socket buffers' by SNMP
Message-ID:  <fef04bda-6aa0-4a80-8999-867b9f37d766@otcnet.ru>
In-Reply-To: <6c780827-e764-8053-356b-a921e0892c15@grosbein.net>
References:  <388da9a7-7b89-89b2-54eb-17d0e818c924@otcnet.ru> <4e41c1d2-19bc-0345-0b03-526e4cb785c7@otcnet.ru> <b279e676-c789-2978-98a0-b8a4b164a111@grosbein.net> <a69d872a-f21e-de66-7677-58beccb0f023@otcnet.ru> <6c780827-e764-8053-356b-a921e0892c15@grosbein.net>

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On 30/12/2020 12:57, Eugene Grosbein wrote:
> 30.12.2020 16:44, Victor Gamov wrote:
> 
>> Currently I'm thinking about ethernet flow control: Host-B connected to VLAN-750 on the third switch has 1G link (via igb driver)
>> and both Host-A and Host-B has fc=3.  So when Host-B get microburst it can send PAUSE and Host-A start to fill queue.
>> But FC disabled for all switches and I'm not sure about PAUSE can be propagated from Host-A to Host-B
> 
> AFAIK, pause frames are not forwarded. For short term you should make flow control settings consistent
> between link partners,

As I understand hw.ix.flow_control=3 to allow flow-control for 
negotiation.  Real PAUSE setting will be set during negotiation.  So 
where I can find active flow-control setting for host interface?

> maybe increase kern.ipc.maxsockbuf and then net.inet.udp.recvspace.

Eugene, at first message you suppose Host-A (sender) "outgoing link for 
that UDP packets is congested" because this host shows non-zero "dropped 
due to full socket buffers".   So is net.inet.udp.recvspace increasing 
on Host-B (mainly receiver) will be affected for this congestion?  Or I 
need to try to increase both kern.ipc.maxsockbuf and 
net.inet.udp.recvspace on both hosts?

Also how I can check current sockbuf usage?

> But for long term you should consider adding more links and create LACP aggregate
> so not input nor output link be close to congestion.

I'll migrate to 10G on Host-B at next month.


Thanks for your advise!

-- 
CU,
Victor Gamov



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