From owner-svn-src-head@FreeBSD.ORG Fri May 30 15:39:27 2014 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id ACF6A3FE; Fri, 30 May 2014 15:39:27 +0000 (UTC) Received: from mail-wi0-x22a.google.com (mail-wi0-x22a.google.com [IPv6:2a00:1450:400c:c05::22a]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 8462F225E; Fri, 30 May 2014 15:39:26 +0000 (UTC) Received: by mail-wi0-f170.google.com with SMTP id bs8so1305383wib.3 for ; Fri, 30 May 2014 08:39:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:reply-to:sender:in-reply-to:references:date:message-id :subject:from:to:cc:content-type; bh=XFfergtBrahqAx0gLPRgMWCyBq7DXhaci2waVfrEveI=; b=E7omFOhegiluWDod5SDxpGveicp5juMWdsz0DDUbHZQ0Si8HqJcVL1B3JwnzhuImBl vrkeDdFqr9+vB4gBqyIfbMEXjxdMx203LSo/zoG94Fg1snqoPjgSaJTgIraJI1jPEb2P WzdtwhGBtPHjhLIB7aB6n91I8L0gEL6lJr3YGO7Fkkjl/DQqZEgUiJx1va88/ovHJ9N7 ++z/RxuRWL+jc659JBBUwF+mN51lqZbJA3MAoo9QT0IB38ZhQQWFiaxo/wE4qGN8TMQh o1P4XiWwhs+SIbchHdC0Xtjm2syGDf1p6TimVdgr4ynMgHFgl/vxQNS4zw3T9lc/ZITA m2sg== MIME-Version: 1.0 X-Received: by 10.181.8.67 with SMTP id di3mr7980138wid.8.1401464364461; Fri, 30 May 2014 08:39:24 -0700 (PDT) Reply-To: attilio@FreeBSD.org Sender: asmrookie@gmail.com Received: by 10.217.61.196 with HTTP; Fri, 30 May 2014 08:39:24 -0700 (PDT) In-Reply-To: <201405301103.11980.jhb@freebsd.org> References: <201405272131.s4RLVBEU035321@svn.freebsd.org> <201405301103.11980.jhb@freebsd.org> Date: Fri, 30 May 2014 17:39:24 +0200 X-Google-Sender-Auth: HKaN189w69ALy1IAhkHkLSetnwU Message-ID: Subject: Re: svn commit: r266775 - head/sys/x86/x86 From: Attilio Rao To: John Baldwin Content-Type: text/plain; charset=UTF-8 Cc: "src-committers@freebsd.org" , Benno Rice , "svn-src-all@freebsd.org" , Scott Long , "svn-src-head@freebsd.org" , "Peel, Casey" X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 30 May 2014 15:39:27 -0000 On Fri, May 30, 2014 at 5:03 PM, John Baldwin wrote: > On Friday, May 30, 2014 10:54:06 am Attilio Rao wrote: >> On Tue, May 27, 2014 at 11:31 PM, Scott Long wrote: >> > Author: scottl >> > Date: Tue May 27 21:31:11 2014 >> > New Revision: 266775 >> > URL: http://svnweb.freebsd.org/changeset/base/266775 >> > >> > Log: >> > Eliminate the fake contig_dmamap and replace it with a new flag, >> > BUS_DMA_KMEM_ALLOC. They serve the same purpose, but using the flag >> > means that the map can be NULL again, which in turn enables significant >> > optimizations for the common case of no bouncing. >> >> While I think this is in general a good idea, unfortunately our >> drivers do so many dumb things when freeing DMA allocated buffers that >> having a NULL map is going to cause some "turbolence" and make such >> bugs more visible. >> An example is with ATA, where I think this fix is needed: >> http://www.freebsd.org/~attilio/dmamem_free-ata.patch >> >> Otherwise, what can happen with bounce buffers, is that the allocated >> memory via contig malloc was not going to be freed anytime. >> >> I tried to look around and I found questionable (read broken) code in >> basically every driver which allocates DMA buffers, so I really don't >> feel I want to fix the majority of our drivers. I just think such >> paths are not excercised enough to be seen in practice often or the >> bugs just get unnoticed. > > Eh, many maps for static allocations were already NULL and have been for a > long time. This is nothign new. Plus, the diff you posted has a bug > regardless of explicitly destroying a map created by bus_dmamem_alloc(). Did you notice that I *removed* the destroy not *added*? Attilio -- Peace can only be achieved by understanding - A. Einstein