From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: Question about KVM on Big.Little SoC Date: Tue, 6 Sep 2016 09:12:26 +0100 Message-ID: <57CE7A6A.1010508@arm.com> References: <20160906080005.GB5493@linux-7smt.suse> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Peng Fan , andre.przywara@arm.com, christoffer.dall@linaro.org Return-path: Received: from foss.arm.com ([217.140.101.70]:41670 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753716AbcIFIMe (ORCPT ); Tue, 6 Sep 2016 04:12:34 -0400 In-Reply-To: <20160906080005.GB5493@linux-7smt.suse> Sender: kvm-owner@vger.kernel.org List-ID: Peng, On 06/09/16 09:00, Peng Fan wrote: > Hi Andre, > > I came across your patch which try to fix kvm on big.little. > https://lists.cs.columbia.edu/pipermail/kvmarm/2013-April/003989.html > > I am trying KVM on a big.little SoC with 4 A53 and 2 A72. > I wonder whether kvm supports running on big.little SoC now? > > I am checking arch/{arm,arm64}/kvm code, but I think you may give a quick answer. > > And If kvm supports running on big.Little SoC, is it ok for me to pass "-cpu host" > to qemu? Can guest vcpu be scheduled freely on big and little SoCs? > > Would you please kindly give me some clues about where is the piece code to handle > kvm on big.little? The current situation is that: - Yes, KVM works on big-little systems (it always had) - The only useful option you can pass to qemu is "-cpu host" - There is no guarantee that QEMU will even start, unless you constraint its affinity to one single type of CPUs (use taskset). - If you use taskset, there will be no scheduling between types of cores - If you do not, scheduling will happen, but that's a fairly unsafe thing to do (the guest doesn't know it is being migrated between CPUs that may have different behaviours...). Hope this helps, M. -- Jazz is not dead. It just smells funny...