From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: Make QEmu HPET disabled by default for KVM? Date: Thu, 11 Mar 2010 10:31:57 +0200 Message-ID: <20100311083157.GZ16909@redhat.com> References: <201003111552.54293.sheng@linux.intel.com> <4B98A294.7010104@redhat.com> <201003111623.58755.sheng@linux.intel.com> <4B98A99C.8020909@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Sheng Yang , Marcelo Tosatti , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:30431 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755518Ab0CKIcA (ORCPT ); Thu, 11 Mar 2010 03:32:00 -0500 Content-Disposition: inline In-Reply-To: <4B98A99C.8020909@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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. -- Gleb.