Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755243AbZLVT0a (ORCPT ); Tue, 22 Dec 2009 14:26:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755210AbZLVT01 (ORCPT ); Tue, 22 Dec 2009 14:26:27 -0500 Received: from mx1.redhat.com ([209.132.183.28]:31786 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755201AbZLVT01 (ORCPT ); Tue, 22 Dec 2009 14:26:27 -0500 Message-ID: <4B311D20.7020400@redhat.com> Date: Tue, 22 Dec 2009 21:25:20 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.5) Gecko/20091209 Fedora/3.0-4.fc12 Thunderbird/3.0 MIME-Version: 1.0 To: Gregory Haskins CC: Ingo Molnar , kvm@vger.kernel.org, Andrew Morton , torvalds@linux-foundation.org, "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 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> In-Reply-To: <4B311ADA.4000700@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1498 Lines: 40 On 12/22/2009 09:15 PM, 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. > If you're not doing something pretty minor, you're better of waking up a thread (perhaps _sync if you want to keep on the same cpu). With the new user return notifier thingie, that's pretty cheap. > 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. > > It would be easier to add data logging support to ioeventfd, if it was needed that badly. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- 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/