From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [RFC] virtio: use mandatory barriers for remote processor vdevs Date: Fri, 02 Dec 2011 10:56:33 +1030 Message-ID: <8762hzsts6.fsf@rustcorp.com.au> References: <1322569886-13055-1-git-send-email-ohad@wizery.com> <20111129131110.GC19157@redhat.com> <20111129151958.GA31789@redhat.com> <20111130145004.GD21413@redhat.com> <20111130231306.GD30031@redhat.com> <87zkfdrpn8.fsf@rustcorp.com.au> <20111201081236.GB5479@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20111201081236.GB5479@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Thu, 1 Dec 2011 10:12:37 +0200, "Michael S. Tsirkin" wrote: > On Thu, Dec 01, 2011 at 12:58:59PM +1030, Rusty Russell wrote: > > On Thu, 1 Dec 2011 01:13:07 +0200, "Michael S. Tsirkin" wrote: > > > For x86, stores into memory are ordered. So I think that yes, smp_XXX > > > can be selected at compile time. > > > > > > So let's forget the virtio strangeness for a minute, > > > > Hmm, we got away with light barriers because we knew we were not > > *really* talking to a device. But now with virtio-mmio, turns out we > > are :) > > You think virtio-mmio this issue too? It's reported on remoteproc... I think any non-virtual, non-PCI device has to worry about it. Perhaps all virtio-mmio are virtual (at this point). I'm tempted to say we want permission from the device to do relaxed barriers (so I don't have to worry about it!) > > I'm really tempted to revert d57ed95 for 3.2, and we can revisit this > > optimization later if it proves worthwhile. > > Generally it does seem the best we can do for 3.2. > > Given it's rc3, I'd be a bit wary of introducing regressions - I'll try > to find some real setups (as in - not my laptop) to run some benchmarks > on, to verify there's no major problem. > I hope I can report on this in about a week from now - want to hold onto this meanwhile? Yep, no huge hurry. Thanks! Cheers, Rusty. From mboxrd@z Thu Jan 1 00:00:00 1970 From: rusty@rustcorp.com.au (Rusty Russell) Date: Fri, 02 Dec 2011 10:56:33 +1030 Subject: [RFC] virtio: use mandatory barriers for remote processor vdevs In-Reply-To: <20111201081236.GB5479@redhat.com> References: <1322569886-13055-1-git-send-email-ohad@wizery.com> <20111129131110.GC19157@redhat.com> <20111129151958.GA31789@redhat.com> <20111130145004.GD21413@redhat.com> <20111130231306.GD30031@redhat.com> <87zkfdrpn8.fsf@rustcorp.com.au> <20111201081236.GB5479@redhat.com> Message-ID: <8762hzsts6.fsf@rustcorp.com.au> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, 1 Dec 2011 10:12:37 +0200, "Michael S. Tsirkin" wrote: > On Thu, Dec 01, 2011 at 12:58:59PM +1030, Rusty Russell wrote: > > On Thu, 1 Dec 2011 01:13:07 +0200, "Michael S. Tsirkin" wrote: > > > For x86, stores into memory are ordered. So I think that yes, smp_XXX > > > can be selected at compile time. > > > > > > So let's forget the virtio strangeness for a minute, > > > > Hmm, we got away with light barriers because we knew we were not > > *really* talking to a device. But now with virtio-mmio, turns out we > > are :) > > You think virtio-mmio this issue too? It's reported on remoteproc... I think any non-virtual, non-PCI device has to worry about it. Perhaps all virtio-mmio are virtual (at this point). I'm tempted to say we want permission from the device to do relaxed barriers (so I don't have to worry about it!) > > I'm really tempted to revert d57ed95 for 3.2, and we can revisit this > > optimization later if it proves worthwhile. > > Generally it does seem the best we can do for 3.2. > > Given it's rc3, I'd be a bit wary of introducing regressions - I'll try > to find some real setups (as in - not my laptop) to run some benchmarks > on, to verify there's no major problem. > I hope I can report on this in about a week from now - want to hold onto this meanwhile? Yep, no huge hurry. Thanks! Cheers, Rusty. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756419Ab1LBBLD (ORCPT ); Thu, 1 Dec 2011 20:11:03 -0500 Received: from ozlabs.org ([203.10.76.45]:35300 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756358Ab1LBBK6 (ORCPT ); Thu, 1 Dec 2011 20:10:58 -0500 From: Rusty Russell To: "Michael S. Tsirkin" Cc: Ohad Ben-Cohen , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [RFC] virtio: use mandatory barriers for remote processor vdevs In-Reply-To: <20111201081236.GB5479@redhat.com> References: <1322569886-13055-1-git-send-email-ohad@wizery.com> <20111129131110.GC19157@redhat.com> <20111129151958.GA31789@redhat.com> <20111130145004.GD21413@redhat.com> <20111130231306.GD30031@redhat.com> <87zkfdrpn8.fsf@rustcorp.com.au> <20111201081236.GB5479@redhat.com> User-Agent: Notmuch/0.6.1-1 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) Date: Fri, 02 Dec 2011 10:56:33 +1030 Message-ID: <8762hzsts6.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 1 Dec 2011 10:12:37 +0200, "Michael S. Tsirkin" wrote: > On Thu, Dec 01, 2011 at 12:58:59PM +1030, Rusty Russell wrote: > > On Thu, 1 Dec 2011 01:13:07 +0200, "Michael S. Tsirkin" wrote: > > > For x86, stores into memory are ordered. So I think that yes, smp_XXX > > > can be selected at compile time. > > > > > > So let's forget the virtio strangeness for a minute, > > > > Hmm, we got away with light barriers because we knew we were not > > *really* talking to a device. But now with virtio-mmio, turns out we > > are :) > > You think virtio-mmio this issue too? It's reported on remoteproc... I think any non-virtual, non-PCI device has to worry about it. Perhaps all virtio-mmio are virtual (at this point). I'm tempted to say we want permission from the device to do relaxed barriers (so I don't have to worry about it!) > > I'm really tempted to revert d57ed95 for 3.2, and we can revisit this > > optimization later if it proves worthwhile. > > Generally it does seem the best we can do for 3.2. > > Given it's rc3, I'd be a bit wary of introducing regressions - I'll try > to find some real setups (as in - not my laptop) to run some benchmarks > on, to verify there's no major problem. > I hope I can report on this in about a week from now - want to hold onto this meanwhile? Yep, no huge hurry. Thanks! Cheers, Rusty.