netdev - Re: [PATCH v2 net-next] tcp: avoid expensive pskb_expand

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Date:	Thu, 19 Apr 2012 11:05:49 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	Neal Cardwell <ncardwell@...gle.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>,
	Maciej Żenczykowski <maze@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH v2 net-next] tcp: avoid expensive pskb_expand_head() calls


>> That or bare ACKs have to be excluded from the overhead checks somehow I
>> guess, or there be more aggressive copying into smaller buffers.
>>
>
> Nope, we need a limit or risk OOM if a malicious peer send ACK flood ;)

Well, there is that...

>
> To be clear, if I change the tcp_rmem[1] from 87380 to big value, I no
> longer have ACK drops, but still poor performance, I am still
> investigating.

What happens if you set net.core.[rw]mem_max to 4 MB and then use 
something like -s 1M -S 1M in netperf?

netperf -t TCP_STREAM -H <remote> -- -s 1M -S 1M -m 64K

(or -m 16K if you want to keep the send size the same as your previous 
tests...)

rick
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