From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Guest kernel hangs in smp kvm for older kernels prior to tsc sync cleanup Date: Wed, 19 Dec 2007 08:33:39 +0200 Message-ID: <4768BB43.1000609@qumranet.com> References: <47680173.6060606@qumranet.com> <20071218221930.GA26109@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel , linux-kernel To: Ingo Molnar Return-path: In-Reply-To: <20071218221930.GA26109-X9Un+BFzKDI@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Ingo Molnar wrote: >> While the change mentions that it fixes a time warp bug, it also says >> it should be rare. So clearly kvm smp tsc handing is buggy. >> Ingo/Thomas, (or anybody else), do you have any insight as to what kvm >> can be doing wrong to trigger this behavior? >> > > hm. Those time warps were really small, due to the small imperfections > in the "sync up all CPUs to the same moment and do a WRMSR to clear all > their TSCs" mechanism. I.e. at most a few usec time warps. I really dont > know how that should result in udevd hanging. Can you debug udevd in any > way? > > Adding debug didn't help. I'll try some sysrq keys to see what the guest thinks is happening. > so the only thing that KVM might be doing incorrectly here is the > emulation of the WRMSR that clears the TSC of each vcpu? > By inspection, it is correct. Of course I may be missing something, so I'll write a unit test for it. It should also be much slower than the native wrmsr. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- SF.Net email is sponsored by: Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace