From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 4/7] ide: use the PCI memory access interface Date: Thu, 02 Sep 2010 18:24:25 +0300 Message-ID: <4C7FC1A9.3080800@redhat.com> References: <1283007298-10942-1-git-send-email-eduard.munteanu@linux360.ro> <1283007298-10942-5-git-send-email-eduard.munteanu@linux360.ro> <20100902051911.GA4273@redhat.com> <20100902091200.GB7319@localhost> <20100902095813.GB9085@redhat.com> <20100902150135.GA7136@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , joro@8bytes.org, blauwirbel@gmail.com, paul@codesourcery.com, anthony@codemonkey.ws, av1474@comtv.ru, yamahata@valinux.co.jp, kvm@vger.kernel.org, qemu-devel@nongnu.org To: Eduard - Gabriel Munteanu Return-path: Received: from mx1.redhat.com ([209.132.183.28]:23618 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752251Ab0IBPY4 (ORCPT ); Thu, 2 Sep 2010 11:24:56 -0400 In-Reply-To: <20100902150135.GA7136@localhost> Sender: kvm-owner@vger.kernel.org List-ID: On 09/02/2010 06:01 PM, Eduard - Gabriel Munteanu wrote: > On Thu, Sep 02, 2010 at 12:58:13PM +0300, Michael S. Tsirkin wrote: >> On Thu, Sep 02, 2010 at 12:12:00PM +0300, Eduard - Gabriel Munteanu wrote: >>> On Thu, Sep 02, 2010 at 08:19:11AM +0300, Michael S. Tsirkin wrote: >>>> On Sat, Aug 28, 2010 at 05:54:55PM +0300, Eduard - Gabriel Munteanu wrote: >> I don't insist on this solution, but what other way do you propose to >> avoid the overhead for everyone not using an iommu? >> I'm all for a solution that would help iommu as well, >> but one wasn't yet proposed. >> > Hm, we could get even better performance by simply making the IOMMU a > compile-time option. It also avoids problems in case some device hasn't > been converted yet, and involves little to no tradeoffs. What do you > think? > > AFAICT, there are few uses for the IOMMU besides development and > avantgarde stuff, as you note. So distributions can continue supplying > prebuilt QEMU/KVM packages compiled with the IOMMU turned off for the > time being. The only practical (commercial) use right now would be in > the case of private virtual servers, which could be divided further into > nested guests (though real IOMMU hardware isn't widespread yet). > > Blue Swirl, in the light of this, do you agree on making it a > compile-time option? That's not a practical long term solution. Eventually everything gets turned on. I don't really see a problem with the additional indirection. By the time we reach actual hardware to satisfy the request, we'll have gone through many such indirections; modern processors deal very well with them. -- error compiling committee.c: too many arguments to function From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=33053 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OrBep-0006hf-Vo for qemu-devel@nongnu.org; Thu, 02 Sep 2010 11:24:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OrBeo-0006VS-RT for qemu-devel@nongnu.org; Thu, 02 Sep 2010 11:24:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:20311) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OrBeo-0006V5-JD for qemu-devel@nongnu.org; Thu, 02 Sep 2010 11:24:54 -0400 Message-ID: <4C7FC1A9.3080800@redhat.com> Date: Thu, 02 Sep 2010 18:24:25 +0300 From: Avi Kivity MIME-Version: 1.0 References: <1283007298-10942-1-git-send-email-eduard.munteanu@linux360.ro> <1283007298-10942-5-git-send-email-eduard.munteanu@linux360.ro> <20100902051911.GA4273@redhat.com> <20100902091200.GB7319@localhost> <20100902095813.GB9085@redhat.com> <20100902150135.GA7136@localhost> In-Reply-To: <20100902150135.GA7136@localhost> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [PATCH 4/7] ide: use the PCI memory access interface List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduard - Gabriel Munteanu Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" , joro@8bytes.org, qemu-devel@nongnu.org, blauwirbel@gmail.com, yamahata@valinux.co.jp, paul@codesourcery.com On 09/02/2010 06:01 PM, Eduard - Gabriel Munteanu wrote: > On Thu, Sep 02, 2010 at 12:58:13PM +0300, Michael S. Tsirkin wrote: >> On Thu, Sep 02, 2010 at 12:12:00PM +0300, Eduard - Gabriel Munteanu wrote: >>> On Thu, Sep 02, 2010 at 08:19:11AM +0300, Michael S. Tsirkin wrote: >>>> On Sat, Aug 28, 2010 at 05:54:55PM +0300, Eduard - Gabriel Munteanu wrote: >> I don't insist on this solution, but what other way do you propose to >> avoid the overhead for everyone not using an iommu? >> I'm all for a solution that would help iommu as well, >> but one wasn't yet proposed. >> > Hm, we could get even better performance by simply making the IOMMU a > compile-time option. It also avoids problems in case some device hasn't > been converted yet, and involves little to no tradeoffs. What do you > think? > > AFAICT, there are few uses for the IOMMU besides development and > avantgarde stuff, as you note. So distributions can continue supplying > prebuilt QEMU/KVM packages compiled with the IOMMU turned off for the > time being. The only practical (commercial) use right now would be in > the case of private virtual servers, which could be divided further into > nested guests (though real IOMMU hardware isn't widespread yet). > > Blue Swirl, in the light of this, do you agree on making it a > compile-time option? That's not a practical long term solution. Eventually everything gets turned on. I don't really see a problem with the additional indirection. By the time we reach actual hardware to satisfy the request, we'll have gone through many such indirections; modern processors deal very well with them. -- error compiling committee.c: too many arguments to function