size of socket reads that will be offloaded to a DMA copy engine

$cat /proc/sys/net/ipv4/tcp_dma_copybreak
4096
$

tcp_dma_copybreak - INTEGER
Lower limit, in bytes, of the size of socket reads that will be
offloaded to a DMA copy engine, if one is present in the system
and CONFIG_NET_DMA is enabled.
Default: 4096

grepping through linux kernel source 2.6.32
sysctl_net_ipv4.c:              .procname       = "tcp_dma_copybreak",