From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH 2/2] Remove -tdf Date: Wed, 23 Jul 2008 10:31:08 -0500 Message-ID: <48874EBC.1050209@codemonkey.ws> References: <1216756217-21888-1-git-send-email-aliguori@us.ibm.com> <1216756217-21888-2-git-send-email-aliguori@us.ibm.com> <48865934.8070007@qumranet.com> <48868769.7050307@codemonkey.ws> <20080723055825.GA3196@minantech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Dor Laor , kvm@vger.kernel.org, Avi Kivity To: Gleb Natapov Return-path: Received: from yw-out-2324.google.com ([74.125.46.29]:8146 "EHLO yw-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751025AbYGWPbk (ORCPT ); Wed, 23 Jul 2008 11:31:40 -0400 Received: by yw-out-2324.google.com with SMTP id 9so1055251ywe.1 for ; Wed, 23 Jul 2008 08:31:39 -0700 (PDT) In-Reply-To: <20080723055825.GA3196@minantech.com> Sender: kvm-owner@vger.kernel.org List-ID: Gleb Natapov wrote: > On Tue, Jul 22, 2008 at 08:20:41PM -0500, Anthony Liguori wrote: > >>> Currently both in-kernel PIT and even the in kernel irqchips are not >>> 100% bullet proof. >>> Of course this code is a hack, Gleb Natapov has send better fix for >>> PIT/RTC to qemu list. >>> Can you look into them: >>> http://www.mail-archive.com/kvm@vger.kernel.org/msg01181.html >>> >> Paul Brook's initial feedback is still valid. It causes quite a lot of >> churn and may not jive well with a virtual time base. An advantage to >> the current -tdf patch is that it's more contained. I don't think >> either approach is going to get past Paul in it's current form. >> > Yes, my patch causes a lot of churn because it changes widely used API. > Indeed. > But the time drift fix itself is contained to PIT/RTC code only. The > last patch series I've sent disables time drift fix if virtual time base > is enabled as Paul requested. There was no further feedback from him. > I think there's a healthy amount of scepticism about whether tdf really is worth it. This is why I suggested that we need to better quantify exactly how much this patch set helps things. For instance, a time drift test for kvm-autotest would be perfect. tdf is ugly and deviates from how hardware works. A compelling case is needed to justify it. > As Jan Kiszka wrote in one of his mails may be Paul's virtual time base > can be adopted to work with KVM too. BTW how virtual time base handles > SMP guest? > I really don't know. I haven't looked to deeply at the virtual time base. Keep in mind though, that QEMU SMP is not true SMP. All VCPUs run in lock-step. Regards, Anthony Liguori >> Also, it's important that this is reproducible in upstream QEMU and not >> just in KVM. If we can make a compelling case for the importance of >> this, we can possibly work out a compromise. >> >> > I developed and tested my patch with upstream QEMU. > > -- > Gleb. >