Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752839AbZLWBFZ (ORCPT ); Tue, 22 Dec 2009 20:05:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751277AbZLWBFT (ORCPT ); Tue, 22 Dec 2009 20:05:19 -0500 Received: from x35.xmailserver.org ([64.71.152.41]:42620 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751176AbZLWBFR (ORCPT ); Tue, 22 Dec 2009 20:05:17 -0500 X-AuthUser: davidel@xmailserver.org Date: Tue, 22 Dec 2009 17:05:10 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@makko.or.mcafeemobile.com To: Gregory Haskins cc: Avi Kivity , Ingo Molnar , kvm@vger.kernel.org, Andrew Morton , Linus Torvalds , "linux-kernel@vger.kernel.org" , netdev@vger.kernel.org, "alacrityvm-devel@lists.sourceforge.net" Subject: Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33 In-Reply-To: <4B3123AA.8040205@gmail.com> Message-ID: References: <4B1D4F29.8020309@gmail.com> <20091218215107.GA14946@elte.hu> <4B2F9582.5000002@gmail.com> <20091222075742.GB26467@elte.hu> <4B3103B4.4070708@gmail.com> <4B3115C1.4070303@redhat.com> <4B311ADA.4000700@gmail.com> <4B3123AA.8040205@gmail.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc 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 Content-Length: 2316 Lines: 62 On Tue, 22 Dec 2009, Gregory Haskins wrote: > On 12/22/09 2:39 PM, Davide Libenzi wrote: > > On Tue, 22 Dec 2009, Gregory Haskins wrote: > > > >> On 12/22/09 1:53 PM, Avi Kivity wrote: > >>> I asked why the irqfd/ioeventfd mechanisms are insufficient, and you did not reply. > >>> > >> > >> BTW: the ioeventfd issue just fell through the cracks, so sorry about > >> that. Note that I have no specific issue with irqfd ever since the > >> lockless IRQ injection code was added. > >> > >> ioeventfd turned out to be suboptimal for me in the fast path for two > >> reasons: > >> > >> 1) the underlying eventfd is called in atomic context. I had posted > >> patches to Davide to address that limitation, but I believe he rejected > >> them on the grounds that they are only relevant to KVM. > > > > I thought we addressed this already, in the few hundreds of email we > > exchanged back then :) > > We addressed the race conditions, but not the atomic callbacks. I can't > remember exactly what you said, but the effect was "no", so I dropped it. ;) > > This was the thread. > > http://www.archivum.info/linux-kernel@vger.kernel.org/2009-06/08548/Re:_[KVM-RFC_PATCH_1_2]_eventfd:_add_an_explicit_srcu_based_notifier_interface Didn't that ended up in schedule_work() being just fine, and no need was there for pre-emptible callbacks? > >> 2) it cannot retain the data field passed in the PIO. I wanted to have > >> one vector that could tell me what value was written, and this cannot be > >> expressed in ioeventfd. > > > > Like might have hinted in his reply, couldn't you add data support to the > > ioeventfd bits in KVM, instead of leaking them into mainline eventfd? > > > > Perhaps, or even easier I could extend xinterface. Which is what I did ;) > > The problem with the first proposal is that you would no longer actually > have an eventfd based mechanism...so any code using ioeventfd (like > Michael Tsirkin's for instance) would break. At that point, the KVM eventfd can take care of thing so that Michael bits do not break. - Davide -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/