From mboxrd@z Thu Jan 1 00:00:00 1970 From: Beth Kon Subject: Re: The HPET issue on Linux Date: Wed, 06 Jan 2010 14:20:31 -0500 Message-ID: <4B44E27F.6090406@us.ibm.com> References: <201001061748.52689.sheng@linux.intel.com> <20100106100957.GF4905@redhat.com> <4B44648F.2010702@redhat.com> <4B44D82A.9030805@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Gleb Natapov , Sheng Yang , kvm@vger.kernel.org To: dlaor@redhat.com Return-path: Received: from e7.ny.us.ibm.com ([32.97.182.137]:51088 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755934Ab0AFTUY (ORCPT ); Wed, 6 Jan 2010 14:20:24 -0500 Received: from d01relay05.pok.ibm.com (d01relay05.pok.ibm.com [9.56.227.237]) by e7.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id o06JETpf007392 for ; Wed, 6 Jan 2010 14:14:29 -0500 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d01relay05.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o06JKNaP115144 for ; Wed, 6 Jan 2010 14:20:23 -0500 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id o06JKMqF017612 for ; Wed, 6 Jan 2010 12:20:22 -0700 In-Reply-To: <4B44D82A.9030805@us.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Beth Kon wrote: > Dor Laor wrote: >> 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. > I will try to look into this. Since HPET is edge-triggered, looks like > this problem is of a different nature than PIT. Is this a solid > failure or intermittent? Anthony just explained that on x86, even edge-triggered interrupts are queued in the apic and an eoi will occur, so this is not different than the PIT. > >> >>> >>> -- >>> 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 >> >> -- >> 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 > > -- Regards, Beth Kon