From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=44274 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PmSYU-0005VW-88 for qemu-devel@nongnu.org; Mon, 07 Feb 2011 09:59:07 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PmSYT-0007go-Bx for qemu-devel@nongnu.org; Mon, 07 Feb 2011 09:59:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52386) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PmSYT-0007gY-37 for qemu-devel@nongnu.org; Mon, 07 Feb 2011 09:59:05 -0500 Message-ID: <4D5008B3.90505@redhat.com> Date: Mon, 07 Feb 2011 16:58:59 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [RFC: 0/2] patch for QEMU HPET periodic timer emulation to alleviate time drift 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> In-Reply-To: <4D5007B9.7060806@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Jan Kiszka , Glauber Costa , Ulrich Obergfell , kvm , qemu-devel On 02/07/2011 04:54 PM, Anthony Liguori wrote: > >> Why the accumulated_ticks argument? > > Then the missing ticks is stored in the PeriodicTimer instead of > storing it in the device state. That means we won't forget to save it > in vmstate. > > It's convenient because then if we lose ticks in the PeriodicTimer > layer, the devices have instance access to that info. When you do a > read() from timerfd, it returns the number of coalesced events. > That's the interface I had in my mind. > > We could just add a getter for PeriodicTimer and it would serve the > same purpose. If a drift compensation policy is in effect, you don't need the missed ticks, since you will get one callback for each (delayed) tick. If there is no drift compensation policy, presumably you aren't interested in lost ticks. So the ticks argument isn't very useful. 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. -- error compiling committee.c: too many arguments to function