From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Guest kernel hangs in smp kvm for older kernels prior to tsc sync cleanup Date: Tue, 18 Dec 2007 19:20:51 +0200 Message-ID: <47680173.6060606@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel , linux-kernel To: Ingo Molnar , Thomas Gleixner Return-path: 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 Booting RHEL 5 i386 in kvm with -no-kvm-irqchip -smp 4 will hang in udev. I bisected this to a change in the _guest_ kernel: > commit 95492e4646e5de8b43d9a7908d6177fb737b61f0 > Author: Ingo Molnar > Date: Fri Feb 16 01:27:34 2007 -0800 > > [PATCH] x86: rewrite SMP TSC sync code > > make the TSC synchronization code more robust, and unify it > between x86_64 and > i386. > > The biggest change is the removal of the 'fix up TSCs' code on > x86_64 and > i386, in some rare cases it was /causing/ time-warps on SMP systems. > > The new code only checks for TSC asynchronity - and if it can prove a > time-warp (if it can observe the TSC going backwards when going > from one CPU > to another within a critical section), then the TSC clock-source > is turned > off. > > The TSC synchronization-checking code also got moved into a > separate file. So, guest kernels prior to this commit will hang in kvm smp; after this commit they will boot fine. 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? -- 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