From mboxrd@z Thu Jan 1 00:00:00 1970 From: Evgeniy Polyakov Subject: Re: tbench wrt. loopback TSO Date: Sun, 26 Oct 2008 15:34:42 +0300 Message-ID: <20081026123442.GA31506@ioremap.net> References: <20081015.171408.193701292.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, efault@gmx.de, mingo@elte.hu, a.p.zijlstra@chello.nl, herbert@gondor.apana.org.au To: David Miller Return-path: Received: from broadrack.ru ([195.178.208.66]:48855 "EHLO tservice.net.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751944AbYJZMep (ORCPT ); Sun, 26 Oct 2008 08:34:45 -0400 Content-Disposition: inline In-Reply-To: <20081015.171408.193701292.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: Hi. On Wed, Oct 15, 2008 at 05:14:08PM -0700, David Miller (davem@davemloft.net) wrote: > > I got curious about this aspect of the investigation so I wanted > to see it first-hand :-) > > To be honest, this reported effect of disabling TSO in the loopback > driver surprised me because: > > 1) If the benchmark is doing small writes, TSO should have zero > effect. The TSO logic won't kick in. But GSO will try to create a huge packet and that overhead will not be overweighted? That's what I got with the current tree for 8 threads on a 4-way 32-bit Xeons (2 physical CPUs) and 8gb of ram: gso/tso off: 361.367 tso/gso on: 354.635 Disabled/enabled via ethtools: -k tso off/on gso off/on > 2) If larger than MTU writes are being done, TSO should help, > and this is supported by other benchmarks :-) Yes, that's where it is useful. -- Evgeniy Polyakov