From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] NET_DMA: free skbs periodically Date: Sat, 20 Mar 2010 14:29:20 -0700 (PDT) Message-ID: <20100320.142920.242147630.davem@davemloft.net> References: <1268752964-4397-1-git-send-email-steve@digidescorp.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, kuznet@ms2.inr.ac.ru, pekkas@netcore.fi, jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net, linux-kernel@vger.kernel.org To: steve@digidescorp.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:46934 "EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751231Ab0CTV25 (ORCPT ); Sat, 20 Mar 2010 17:28:57 -0400 In-Reply-To: <1268752964-4397-1-git-send-email-steve@digidescorp.com> Sender: netdev-owner@vger.kernel.org List-ID: From: "Steven J. Magnani" Date: Tue, 16 Mar 2010 10:22:44 -0500 > Under NET_DMA, data transfer can grind to a halt when userland issues a > large read on a socket with a high RCVLOWAT (i.e., 512 KB for both). > This appears to be because the NET_DMA design queues up lots of memcpy > operations, but doesn't issue or wait for them (and thus free the > associated skbs) until it is time for tcp_recvmesg() to return. > The socket hangs when its TCP window goes to zero before enough data is > available to satisfy the read. > > Periodically issue asynchronous memcpy operations, and free skbs for ones > that have completed, to prevent sockets from going into zero-window mode. > > Signed-off-by: Steven J. Magnani Applied, thanks for fixing this bug Steven.