From: Willy Tarreau <w@1wt.eu>
Date: Sun, 2 Dec 2012 11:49:27 +0000 (+0000)
Subject: tcp: don't abort splice() after small transfers
X-Git-Tag: omap-for-v3.8/fixes-for-merge-window-v4-signed~45^2~120
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=02275a2ee7c0ea475b6f4a6428f5df592bc9d30b;p=pandora-kernel.git

tcp: don't abort splice() after small transfers

TCP coalescing added a regression in splice(socket->pipe) performance,
for some workloads because of the way tcp_read_sock() is implemented.

The reason for this is the break when (offset + 1 != skb->len).

As we released the socket lock, this condition is possible if TCP stack
added a fragment to the skb, which can happen with TCP coalescing.

So let's go back to the beginning of the loop when this happens,
to give a chance to splice more frags per system call.

Doing so fixes the issue and makes GRO 10% faster than LRO
on CPU-bound splice() workloads instead of the opposite.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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