From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dor Laor Subject: Re: The HPET issue on Linux Date: Wed, 06 Jan 2010 12:23:11 +0200 Message-ID: <4B44648F.2010702@redhat.com> References: <201001061748.52689.sheng@linux.intel.com> <20100106100957.GF4905@redhat.com> Reply-To: dlaor@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Sheng Yang , Beth Kon , kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:56975 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932107Ab0AFKWp (ORCPT ); Wed, 6 Jan 2010 05:22:45 -0500 In-Reply-To: <20100106100957.GF4905@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 01/06/2010 12:09 PM, Gleb Natapov wrote: > On Wed, Jan 06, 2010 at 05:48:52PM +0800, Sheng Yang wrote: >> Hi Beth >> >> I still found the emulated HPET would result in some boot failure. For >> example, on my 2.6.30, with HPET enabled, the kernel would fail check_timer(), >> especially in timer_irq_works(). >> >> The testing of timer_irq_works() is let 10 ticks pass(using mdelay()), and >> want to confirm the clock source with at least 5 ticks advanced in jiffies. >> I've checked that, on my machine, it would mostly get only 4 ticks when HPET >> enabled, then fail the test. On the other hand, if I using PIT, it would get >> more than 10 ticks(maybe understandable if some complementary ticks there). Of >> course, extend the ticks count/mdelay() time can work. >> >> I think it's a major issue of HPET. And it maybe just due to a too long >> userspace path for interrupt injection... If it's true, I think it's not easy >> to deal with it. >> > PIT tick are reinjected automatically, HPET should probably do the same > although it may just create another set of problems. Older Linux do automatic adjustment for lost ticks so automatic reinjection causes time to run too fast. This is why we added the -no-kvm-pit-reinject flag... It took lots of time to pit/rtc to stabilize, in order of seriously consider the hpet emulation, lots of testing should be done. > > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html