From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=54367 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OYCfO-0007Jr-Jv for qemu-devel@nongnu.org; Mon, 12 Jul 2010 02:39:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OYCZq-0007k0-Rb for qemu-devel@nongnu.org; Mon, 12 Jul 2010 02:33:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:64920) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OYCZq-0007jr-JL for qemu-devel@nongnu.org; Mon, 12 Jul 2010 02:33:18 -0400 Message-ID: <4C3AB728.7050406@redhat.com> Date: Mon, 12 Jul 2010 09:33:12 +0300 From: Avi Kivity MIME-Version: 1.0 References: <20100711180910.20121.93313.stgit@localhost6.localdomain6> <20100711180936.20121.35376.stgit@localhost6.localdomain6> <4C3A09F3.8010304@redhat.com> <1278872784.20397.18.camel@x201> <4C3A0DE3.8010806@redhat.com> In-Reply-To: <4C3A0DE3.8010806@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [RFC PATCH 4/5] APIC/IOAPIC EOI callback List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alex Williamson Cc: chrisw@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, pugs@cisco.com On 07/11/2010 09:30 PM, Avi Kivity wrote: >> Registering an eventfd for the eoi seems like a reasonable alternative. > > I'm worried about that racing (with what?) I don't think there's a problem. First, the EOI message is itself asynchronous. While the write to the local APIC is synchronous, effects on the rest of the system are effected using an APIC message, which travels asynchronously. Second, a component that needs timely information doesn't have to wait; it can read the eventfd and be sure it has seen all EOIs up to now. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.