netdev - Re: [PATCH] tcp: avoid wakeups for pure ACK

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Message-Id: <20130228.153807.1427421999295174182.davem@davemloft.net>
Date:	Thu, 28 Feb 2013 15:38:07 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, ncardwell@...gle.com, therbert@...gle.com,
	ycheng@...gle.com, ak@...ux.intel.com
Subject: Re: [PATCH] tcp: avoid wakeups for pure ACK

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 27 Feb 2013 09:05:03 -0800

> TCP prequeue mechanism purpose is to let incoming packets
> being processed by the thread currently blocked in tcp_recvmsg(),
> instead of behalf of the softirq handler, to better adapt flow
> control on receiver host capacity to schedule the consumer.
> 
> But in typical request/answer workloads, we send request, then
> block to receive the answer. And before the actual answer, TCP
> stack receives the ACK packets acknowledging the request.
> 
> Processing pure ACK on behalf of the thread blocked in tcp_recvmsg()
> is a waste of resources, as thread has to immediately sleep again
> because it got no payload.
> 
> This patch avoids the extra context switches and scheduler overhead.
 ...
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.
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