From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Simek Subject: Re: net: more accurate skb truesize - regression on Microblaze Date: Tue, 10 Apr 2012 10:36:57 +0200 Message-ID: <4F83F129.5040502@monstr.eu> References: <4F83EB0E.4020104@monstr.eu> <1334046444.3126.12.camel@edumazet-glaptop> Reply-To: monstr@monstr.eu Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, John Williams , David Miller To: Eric Dumazet Return-path: Received: from mail-ee0-f46.google.com ([74.125.83.46]:33905 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752827Ab2DJIhC (ORCPT ); Tue, 10 Apr 2012 04:37:02 -0400 Received: by eekc41 with SMTP id c41so1244378eek.19 for ; Tue, 10 Apr 2012 01:37:01 -0700 (PDT) In-Reply-To: <1334046444.3126.12.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On 04/10/2012 10:27 AM, Eric Dumazet wrote: > On Tue, 2012-04-10 at 10:10 +0200, Michal Simek wrote: >> Hi Eric, >> >> I have spent some time to investigate what it is causing regression on our network bechmark >> and I have identified that your patch "net: more accurate skb truesize" is causing that. >> >> I see regression especially on incoming tcp (RX) connection which is 20%. On TX I see regression till 5%. >> >> In general microblaze systems are pretty sensitive for memory usage and working with it. >> Increasing packet sizes has big impact on performance. >> I was surprised that regression is so high. >> >> From microblaze point of view is more important to remove that performance regression >> than having more accurate memory accounting. 20% performance regression is simple so high >> for that. >> Isn't there any other way to doing better memory accounting? >> Or is there any workaround which would be possible to use? >> >> Thanks, >> Michal >> > > Hi Michal > > We are currently working on the issue. > > TCP stack was a bit optimistic in the ideal skb->len / skb->truesize > ratio that happened to 'mostly work' before my patch, but not anymore > after it. > > memory accounting was wrong, we really wanted to be accurate, or risk > OOM and crashes. > > Now we must fix tcp. > > In the meantime you could try : > > echo 1>/proc/sys/net/ipv4/tcp_adv_win_scale will retest it and let you know. Thanks, Michal -- Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/ Microblaze U-BOOT custodian