From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sous-sol.org ([216.99.217.87]:57655 "EHLO sequoia.sous-sol.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754890Ab1KLAvL (ORCPT ); Fri, 11 Nov 2011 19:51:11 -0500 Date: Fri, 11 Nov 2011 16:51:00 -0800 From: Chris Wright To: Roland Dreier Cc: David Woodhouse , Alex Williamson , iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, chrisw@sous-sol.org, ddutile@redhat.com Subject: Re: [PATCH] intel-iommu: Default to non-coherent for domains unattached to iommus Message-ID: <20111112005100.GR14486@sequoia.sous-sol.org> References: <20111111224849.9756.13368.stgit@bling.home> <1321058267.2006.21.camel@shinybook.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-pci-owner@vger.kernel.org List-ID: * Roland Dreier (roland@purestorage.com) wrote: > On Fri, Nov 11, 2011 at 4:37 PM, David Woodhouse wrote: > > This brain-damage only affects the first chipsets > > from before we worked out that cache incoherency was a *really* f*cking > > stupid idea, doesn't it? > > As we talked about at KS, I have some Westmere EP (ie latest > and greatest server platform) systems where the BIOS exposes > an option that allows choosing VT-d coherency on or off, and > defaults it to "off". That's just more brain damage AFAICT. Esp. if you do performance testing (and choose not to use passthrough mode)... have and it's quite measurable. I switched default to on long time ago, w/out issue. > What is the "official" Intel line on coherency with Westmere and > Tylersburg -- because as I also mentioned, I was seeing some > problems with VT-d and the default "coherency off" setting that > looked like the IOMMU HW is getting stale PTEs (ie a missing > or not working cache flush). That sounds like sw bugs more than official recommendation issue. thanks, -chris