netdev - Re: [PATCH net-next] tcp: avoid frag allocation for small frames

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Date:	Tue, 29 Nov 2011 13:23:29 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, subramanian.vijay@...il.com
Subject: Re: [PATCH net-next] tcp: avoid frag allocation for small frames

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 29 Nov 2011 09:41:47 +0100

> tcp_sendmsg() uses select_size() helper to choose skb head size when a
> new skb must be allocated.
> 
> If GSO is enabled for the socket, current strategy is to force all
> payload data to be outside of headroom, in PAGE fragments.
> 
> This strategy is not welcome for small packets, wasting memory.
> 
> Experiments show that best results are obtained when using 2048 bytes
> for skb head (This includes the skb overhead and various headers)
> 
> This patch provides better len/truesize ratios for packets sent to
> loopback device, and reduce memory needs for in-flight loopback packets,
> particularly on arches with big pages.
> 
> If a sender sends many 1-byte packets to an unresponsive application,
> receiver rmem_alloc will grow faster and will stop queuing these packets
> sooner, or will collapse its receive queue to free excess memory.
> 
> netperf -t TCP_RR results are improved by ~4 %, and many workloads are
> improved as well (tbench, mysql...)
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Applied.
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