From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] Re: [RFC: 0/2] patch for QEMU HPET periodic timer emulation to alleviate time drift Date: Mon, 07 Feb 2011 17:08:44 +0200 Message-ID: <4D500AFC.4040206@redhat.com> References: <480481933.225059.1296734409954.JavaMail.root@zmail07.collab.prod.int.phx2.redhat.com> <1375835067.226263.1296740625327.JavaMail.root@zmail07.collab.prod.int.phx2.redhat.com> <4D4AC99A.2070803@siemens.com> <4D4B0B07.2040904@codemonkey.ws> <4D4B1CF8.8040800@web.de> <4D4B5F23.7040801@codemonkey.ws> <4D4BBF55.9060000@web.de> <4D4FE6BF.5080502@redhat.com> <4D4FEF81.1040603@codemonkey.ws> <4D4FF02F.2030309@redhat.com> <4D4FF24A.7000004@codemonkey.ws> <4D4FFD3B.2030903@siemens.com> <4D5001A0.8020503@codemonkey.ws> <4D5004FC.80000@siemens.com> <4D5007B9.7060806@codemonkey.ws> <4D5008B3.90505@redhat.com> <4D50094D.1040003@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , Ulrich Obergfell , Glauber Costa , kvm , qemu-devel To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:34912 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753309Ab1BGPIv (ORCPT ); Mon, 7 Feb 2011 10:08:51 -0500 In-Reply-To: <4D50094D.1040003@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 02/07/2011 05:01 PM, Jan Kiszka wrote: > > > > On the other hand, we need a way to inject lost ticks into a > > PeriodicTimer. If interrupt injection detects that an interrupt was > > coalesced, we want the timer to schedule a new tick for us. > > Isn't absence of corresponding call to periodic_timer_ack() sufficient? It probably is. However, that API is easy to misuse; if you forget to call it, the timer goes crazy. The default behaviour should be to assume an ack and the API should provide adjustments. Also need to design the API carefully for changing frequency (Windows is known to do that) and switching from periodic to single shot. For the first case I guess we need to adjust the deferred ticks to the new time base (so if the frequency doubles, the lost ticks up to that point double as well). For the second case, I guess we just lose time. -- error compiling committee.c: too many arguments to function