From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [RFC][NET_SCHED] explict hold dev tx lock Date: Sun, 16 Sep 2007 12:31:58 -0700 (PDT) Message-ID: <20070916.123158.92582301.davem@davemloft.net> References: <1189959274.4241.30.camel@localhost> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: herbert@gondor.apana.org.au, netdev@vger.kernel.org, kaber@trash.net, dada1@cosmosbay.com, johnpol@2ka.mipt.ru To: hadi@cyberus.ca Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:36715 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751957AbXIPTb6 (ORCPT ); Sun, 16 Sep 2007 15:31:58 -0400 In-Reply-To: <1189959274.4241.30.camel@localhost> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: jamal Date: Sun, 16 Sep 2007 12:14:34 -0400 > Changes: > I made changes to the code path as defined in the patch included to > and noticed a slight increase (2-3%) in performance with both e1000 and > tg3; which was a relief because i thought the spinlock_irq (which is > needed because some drivers grab tx lock in interupts) may have negative > effects. The fact it didnt reduce performance was a good thing. > Note: This is the highest end machine ive ever laid hands on, so this > may be misleading. > > So - what side effects do people see in doing this? If none, i will > clean it up and submit. I tried this 4 years ago, it doesn't work. :-) Many drivers, particularly very old ones that PIO packets into a device which can take a long time, absolutely depend upon interrupts being enabled fully during ->hard_start_xmit() so that other high periority devices (such as simpler serial controllers) can have their interrupts serviced during this slow operation. I don't think we want to do it anyways, whatever performance we gain from it is offset by the badness of disabling interrupts during this reasonably length stretch of code. The -rt folks as a result would notice this too and spank us :-)