From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: The HPET issue on Linux Date: Wed, 06 Jan 2010 13:23:28 -0600 Message-ID: <4B44E330.4080805@codemonkey.ws> References: <201001061748.52689.sheng@linux.intel.com> <20100106100957.GF4905@redhat.com> <4B44648F.2010702@redhat.com> <4B44D82A.9030805@us.ibm.com> <4B44E27F.6090406@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: dlaor@redhat.com, Gleb Natapov , Sheng Yang , kvm@vger.kernel.org To: Beth Kon Return-path: Received: from mail-yw0-f176.google.com ([209.85.211.176]:34965 "EHLO mail-yw0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932445Ab0AFTXg (ORCPT ); Wed, 6 Jan 2010 14:23:36 -0500 Received: by ywh6 with SMTP id 6so17730456ywh.4 for ; Wed, 06 Jan 2010 11:23:35 -0800 (PST) In-Reply-To: <4B44E27F.6090406@us.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On 01/06/2010 01:20 PM, Beth Kon wrote: > Beth Kon wrote: >> I will try to look into this. Since HPET is edge-triggered, looks >> like this problem is of a different nature than PIT. Is this a solid >> failure or intermittent? > Anthony just explained that on x86, even edge-triggered interrupts are > queued in the apic and an eoi will occur, so this is not different > than the PIT. Not quite queued in the sense that multiple events will be delivered in order, but I think the point is that you can still detect whether delivery succeeded by counting APIC EOIs. The trouble is that historically we've struggled with doing this in userspace. Maybe it's time to revisit. Regards, Anthony Liguori