Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753481AbZAIPnw (ORCPT ); Fri, 9 Jan 2009 10:43:52 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751635AbZAIPnk (ORCPT ); Fri, 9 Jan 2009 10:43:40 -0500 Received: from gw1.cosmosbay.com ([86.65.150.130]:37896 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751185AbZAIPnj convert rfc822-to-8bit (ORCPT ); Fri, 9 Jan 2009 10:43:39 -0500 Message-ID: <49677074.5090802@cosmosbay.com> Date: Fri, 09 Jan 2009 16:42:44 +0100 From: Eric Dumazet User-Agent: Thunderbird 2.0.0.19 (Windows/20081209) MIME-Version: 1.0 To: David Miller CC: ben@zeus.com, w@1wt.eu, jarkao2@gmail.com, mingo@elte.hu, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, jens.axboe@oracle.com Subject: Re: [PATCH] tcp: splice as many packets as possible at once References: <20090108173028.GA22531@1wt.eu> <49667534.5060501@zeus.com> <20090108.135515.85489589.davem@davemloft.net> <4966F2F4.9080901@cosmosbay.com> In-Reply-To: <4966F2F4.9080901@cosmosbay.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-1.6 (gw1.cosmosbay.com [0.0.0.0]); Fri, 09 Jan 2009 16:42:48 +0100 (CET) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2358 Lines: 51 Eric Dumazet a ?crit : > David Miller a ?crit : >> I'm not applying this until someone explains to me why >> we should remove this test from the splice receive but >> keep it in the tcp_recvmsg() code where it has been >> essentially forever. Reading again tcp_recvmsg(), I found it already is able to eat several skb even in nonblocking mode. setsockopt(5, SOL_SOCKET, SO_RCVLOWAT, [61440], 4) = 0 ioctl(5, FIONBIO, [1]) = 0 poll([{fd=5, events=POLLIN, revents=POLLIN}], 1, -1) = 1 recv(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 65536, MSG_DONTWAIT) = 65536 write(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 65536) = 65536 poll([{fd=5, events=POLLIN, revents=POLLIN}], 1, -1) = 1 recv(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 65536, MSG_DONTWAIT) = 65536 write(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 65536) = 65536 poll([{fd=5, events=POLLIN, revents=POLLIN}], 1, -1) = 1 recv(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 65536, MSG_DONTWAIT) = 65536 write(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 65536) = 65536 poll([{fd=5, events=POLLIN, revents=POLLIN}], 1, -1) = 1 recv(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 65536, MSG_DONTWAIT) = 65536 write(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 65536) = 65536 David, if you referred to code at line 1374 of net/ipv4/tcp.c, I believe there is no issue with it. We really want to break from this loop if !timeo . Willy patch makes splice() behaving like tcp_recvmsg(), but we might call tcp_cleanup_rbuf() several times, with copied=1460 (for each frame processed) I wonder if the right fix should be done in tcp_read_sock() : this is the one who should eat several skbs IMHO, if we want optimal ACK generation. We break out of its loop at line 1246 if (!desc->count) /* this test is always true */ break; (__tcp_splice_read() set count to 0, right before calling tcp_read_sock()) So code at line 1246 (tcp_read_sock()) seems wrong, or pessimistic at least. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/