From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756006Ab0CIUpP (ORCPT ); Tue, 9 Mar 2010 15:45:15 -0500 Received: from mail.digidescorp.com ([66.244.163.200]:41468 "EHLO digidescorp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755100Ab0CIUpL (ORCPT ); Tue, 9 Mar 2010 15:45:11 -0500 X-Spam-Processed: digidescorp.com, Tue, 09 Mar 2010 14:45:10 -0600 X-Authenticated-Sender: steve@digidescorp.com X-Return-Path: prvs=1684ea2dd6=steve@digidescorp.com X-Envelope-From: steve@digidescorp.com Subject: tcp_recvmesg hang under NET_DMA From: "Steven J. Magnani" Reply-To: steve@digidescorp.com To: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, "David S. Miller" Content-Type: text/plain Organization: Digital Design Corporation Date: Tue, 09 Mar 2010 14:44:59 -0600 Message-Id: <1268167499.2985.32.camel@iscandar.digidescorp.com> Mime-Version: 1.0 X-Mailer: Evolution 2.26.3 (2.26.3-1.fc11) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I've run into a case where using NET_DMA seems to cause a PUT to a modified ftpd to hang. AFAICT this is 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. In a case where userland requests a large read (as is the case in my modified ftpd), packet transfer can grind to a halt because so many packets are buffered up and there is no event that causes them to be freed. I can submit a patch that would issue pending memcpys and clean up completed ones around tcp_recvmsg's call to sk_wait_data(), but first I wanted to understand the design better. Were there specific reasons for deferring the async operations so long? Thanks, ------------------------------------------------------------------------ Steven J. Magnani "I claim this network for MARS! www.digidescorp.com Earthling, return my space modulator!" #include