From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [PATCH 00/18] KVM: PPC: Virtualize Gekko guests Date: Tue, 09 Feb 2010 12:00:25 +0100 Message-ID: <4B714049.7010201@suse.de> References: <1265298925-31954-1-git-send-email-agraf@suse.de> <4B6EB7F6.10304@redhat.com> <4B6EE8B2.80009@redhat.com> <4B6F3890.8090401@suse.de> <4B6FD118.2090207@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "kvm-ppc@vger.kernel.org" , "kvm@vger.kernel.org" To: Avi Kivity Return-path: Received: from cantor.suse.de ([195.135.220.2]:42535 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754062Ab0BILA0 (ORCPT ); Tue, 9 Feb 2010 06:00:26 -0500 In-Reply-To: <4B6FD118.2090207@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > On 02/08/2010 12:02 AM, Alexander Graf wrote: >> >>> It's not a good idea for the kernel either, if it happens all the >>> time. If a typical Gekko application uses the fpu and the emulated >>> instructions intensively, performance will suck badly (as in: qemu/tcg >>> will be faster). >>> >>> >> Yeah, I haven't really gotten far enough to run full-blown guests yet. >> So far I'm on demos and they look pretty good. >> >> But as far as intercept speed goes - I just tried running this little >> piece of code in kvmctl: >> >> .global _start >> _start: >> li r3, 42 >> mtsprg 0, r3 >> mfsprg r4, 0 >> b _start >> >> and measured the amount of exits I get on my test machine: >> >> processor : 0 >> cpu : PPC970MP, altivec supported >> clock : 2500.000000MHz >> revision : 1.1 (pvr 0044 0101) >> >> ---> >> >> exits 1811108 >> >> I have no idea how we manage to get that many exits, but apparently we >> are. So I'm less concerned about the speed of the FPU rerouting at the >> moment. >> > > That's pretty impressive (never saw x86 with this exit rate) but it's > more than 1000 times slower than the hardware, assuming 1 fpu IPC (and > the processor can probably do more). An fpu intensive application > will slow to a crawl. Measuring a typical Gekko application, I get about 200k-250k of fpu (incl. paired singles) instructions per second. Alex