From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Make QEmu HPET disabled by default for KVM? Date: Thu, 11 Mar 2010 10:36:09 +0200 Message-ID: <4B98AB79.3090906@redhat.com> References: <201003111552.54293.sheng@linux.intel.com> <4B98A294.7010104@redhat.com> <201003111623.58755.sheng@linux.intel.com> <4B98A99C.8020909@redhat.com> <20100311083157.GZ16909@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Sheng Yang , Marcelo Tosatti , kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:6200 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753682Ab0CKIgL (ORCPT ); Thu, 11 Mar 2010 03:36:11 -0500 In-Reply-To: <20100311083157.GZ16909@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 03/11/2010 10:31 AM, Gleb Natapov wrote: > On Thu, Mar 11, 2010 at 10:28:12AM +0200, Avi Kivity wrote: > >> On 03/11/2010 10:23 AM, Sheng Yang wrote: >> >>>>> I have kept --no-hpet in my setup for >>>>> months... >>>>> >>>> Any details about the problems? HPET is important to some guests. >>>> >>>> >>> Seems like HPET reaction is too slow to satisfy some guests(for it would >>> replace PIT). >>> >>> Here is the thread last time. >>> >>> http://thread.gmane.org/gmane.comp.emulators.kvm.devel/44899 >>> >>> >> Thanks. We can address this in three ways: first, adjust the guest >> not to do timing related tests when virtualized (since no matter >> what we do, the tests may fail). Second, I think we should >> implement userspace ack notifiers (similar to tpr access notifiers >> already present). Third, we can implement a kernel hpet, which, >> after we solve the zillion bug it introduces, will also give a nice >> performance improvement for hpet intensive workloads. >> >> > Second will not solve the problem. Presence of ack notifiers will not > make HPET interrupt arrive faster. > But it will allow us to compensate for interrupts being coalesced, which may be the root of the problem. -- error compiling committee.c: too many arguments to function