Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751378AbbEZSNR (ORCPT ); Tue, 26 May 2015 14:13:17 -0400 Received: from mail-ie0-f174.google.com ([209.85.223.174]:33432 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750962AbbEZSNP (ORCPT ); Tue, 26 May 2015 14:13:15 -0400 Message-ID: <1432663992.4060.286.camel@edumazet-glaptop2.roam.corp.google.com> Subject: Re: [PATCH] net: tcp: Fix a PTO timing granularity issue From: Eric Dumazet To: Ido Yariv Cc: "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , Nandita Dukkipati , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Ido Yariv Date: Tue, 26 May 2015 11:13:12 -0700 In-Reply-To: <20150526175540.GB13376@WorkStation.home> References: <1432650358-11470-1-git-send-email-ido@wizery.com> <1432657435.4060.267.camel@edumazet-glaptop2.roam.corp.google.com> <20150526170222.GA13376@WorkStation.home> <1432660420.4060.271.camel@edumazet-glaptop2.roam.corp.google.com> <20150526175540.GB13376@WorkStation.home> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1422 Lines: 41 On Tue, 2015-05-26 at 13:55 -0400, Ido Yariv wrote: > Hi Eric, > > > I understand, and I also suspect that having it expire after 9ms will > have very little impact, if at all. > > Since it mainly affects HZ=100 systems, we can simply go with having at > least 2 jiffies on these systems, and leave everything else as is. > > However, if the 10ms has a special meaning (couldn't find reasoning for > it in the RFC), making sure this timer doesn't expire prematurely could > be beneficial. I'm afraid this was not tested on the setup mentioned > above though. > RFC did not explain how 10ms delay was implemented. This is the kind of dark side. RFC are full of 'unsaid things', like OS bugs. What is not said in TLP paper is : linux timers have a 'jiffie' granularity that might be 1/100, 1/250, 1/1000, or even 1/64 on Alpha processors... Fact is : We did TLP implementation and experimentations and paper at the same time, and we do not want to change the current behavior on HZ=1000 hosts. This is the kind of change that would require lot of tests for Google. Please resend your patch so that only HZ <= 100 is changed, we will happily acknowledge it. Thanks -- 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/