From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cruise Huang Subject: a question about the "reord" Date: Fri, 13 Jul 2007 15:26:28 +0800 Message-ID: <46972924.9020605@tom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 7bit Cc: David Miller To: netdev@vger.kernel.org Return-path: Received: from smtpr1.tom.com ([202.108.255.195]:34995 "HELO tom.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1759033AbXGMH5l (ORCPT ); Fri, 13 Jul 2007 03:57:41 -0400 Received: from [192.168.9.92] (unknown [172.24.140.62]) by bjapp32 (Coremail) with SMTP id S4ABnE8pl0YmAIw+.1 for ; Fri, 13 Jul 2007 15:27:21 +0800 (CST) Received: from 192.168.9.92([210.22.111.234]) by bjapp22.tom.com(KBAS Gateway 2.1 2.125e) with ESMTP id local22747.1184311631 for ; Fri Jul 13 15:27:11 2007 +0800 Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Dear all: I'm reading the code about the Congestion Control.Now I'm confused about the variable "reord" in the function tcp_sacktag_write_queue(). The "reord" is initialized as the tp->packets_out, I think, which is a max threshold of the reordering. If it detect a hole or D-SACK ,set the reord to : ---> reord = min(fack_count, reord); Finally,the code may update the reordering by: ---> tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0); The questions are : <1> What's the purpose of the "reord" ? <2> Why use the "((tp->fackets_out + 1) - reord)" to update the reordering. Do I need to study some more RFC about this ? If yes,please tell me ,thanks .