netdev - Re: limited network bandwidth with 3.2.x kernels

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Date:	Thu, 16 Feb 2012 12:22:29 -0500
From:	Neal Cardwell <ncardwell@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, bhutchings@...arflare.com,
	netdev@...r.kernel.org, alekcejk@...glemail.com
Subject: Re: limited network bandwidth with 3.2.x kernels

Our team has also run into issues with GRO/LRO "stretch ACKs", and
their negative impact on TCP performance. We have a patch that we've
been working with that deals with the sender-side issues. It turns out
that neither the ABC nor non-ABC byte counting quite fixes the stretch
ACKs issues.

On the receiver side, the approach of changing tcp_grow_window() and
__tcp_grow_window() to adjust things in terms of actual packet size
rather than a fixed 2*MSS sounds great to me as well.

In terms of the original 3.1 vs 3.2 issue report that started this
thread, I didn't see any evidence of LRO or GRO causing stretch ACKs.
(Alexey, would you be able to confim by running "ethtool -k eth0" on
both kernels?) So it seems that probably the original issue is
unrelated to stretch ACKs?

neal
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