netdev - Re: [PATCH RFC 0/2] xfrm: Remove ancient sleeping code

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Message-ID: <1381881514.2045.82.camel@edumazet-glaptop.roam.corp.google.com>
Date:	Tue, 15 Oct 2013 16:58:34 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH RFC 0/2] xfrm: Remove ancient sleeping code

On Tue, 2013-10-15 at 09:30 +0200, Steffen Klassert wrote:

> Right, that's why I've limited the queue to 100 packets. We can
> queue the SYNs of up to 100 tcp connestions that want to use
> this IPsec state. It surely can happen that we queue multiple
> retransmitted SYNs if the IPsec resolution is slow. But the
> queueing code tries at least to get the packets out before
> the first tcp retransmit. I think there is still room for
> optimizations, maybe reducing the queue lenght or the queue
> timeout to avoid queueing retransmitted SYNs as much as possible.

Note that its totally possible to avoid retransmitting SYN if original
SYN is still in a host queue.

We currently increment a SNMP counter when we detect this, we could
do something else (like not queuing a copy of the packet)

http://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/?id=0e280af026a5662ffd57c4e623b822df1f7f47ff

Another work in progress is to delay RTO arming at the time TCP
packet leaves the host queues, instead of at the enqueue time.



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